Linux Network Administrators Guide

Table of Contents

Preface

Purpose and Audience for This Book

Sources of Information

Documentation Available via FTP
Documentation Available via WWW
Documentation Available Commercially
Linux Journal and Linux Magazine
Linux Usenet Newsgroups
Linux Mailing Lists
Online Linux Support
Linux User Groups
Obtaining Linux

File System Standards

Standard Linux Base

About This Book

The Official Printed Version

Overview

Conventions Used in This Book

Submitting Changes

Acknowledgments

The Hall of Fame

1. Introduction to Networking

History

TCP/IP Networks

Introduction to TCP/IP Networks
Ethernets
Other Types of Hardware
The Internet Protocol
IP Over Serial Lines
The Transmission Control Protocol
The User Datagram Protocol
More on Ports
The Socket Library

UUCP Networks

Linux Networking

Different Streaks of Development
Where to Get the Code

Maintaining Your System

System Security

2. Issues of TCP/IP Networking

Networking Interfaces

IP Addresses

Address Resolution

IP Routing

IP Networks
Subnetworks
Gateways
The Routing Table
Metric Values

The Internet Control Message Protocol

Resolving Host Names

3. Configuringthe NetworkingHardware

Kernel Configuration

Kernel Options in Linux 2.0 and Higher
Kernel Networking Options in Linux 2.0.0 and Higher

A Tour of Linux Network Devices

Ethernet Installation

Ethernet Autoprobing

The PLIP Driver

The PPP and SLIP Drivers

Other Network Types

4. Configuring the Serial Hardware

Communications Software for Modem Links

Introduction to Serial Devices

Accessing Serial Devices

The Serial Device Special Files

Serial Hardware

Using the Configuration Utilities

The setserial Command
The stty Command

Serial Devices and the login: Prompt

Configuring the mgetty Daemon

5. Configuring TCP/IP Networking

Mounting the /proc Filesystem

Installing the Binaries

Setting the Hostname

Assigning IP Addresses

Creating Subnets

Writing hosts and networks Files

Interface Configuration for IP

The Loopback Interface
Ethernet Interfaces
Routing Through a Gateway
Configuring a Gateway
The PLIP Interface
The SLIP and PPP Interfaces
The Dummy Interface
IP Alias

All About ifconfig

The netstat Command

Displaying the Routing Table
Displaying Interface Statistics
Displaying Connections

Checking the ARP Tables

6. Name Service and Resolver Configuration

The Resolver Library

The host.conf File
The nsswitch.conf File
Configuring Name Server Lookups Using resolv.conf
Resolver Robustness

How DNS Works

Name Lookups with DNS
Types of Name Servers
The DNS Database
Reverse Lookups

Running named

The named.boot File
The BIND 8 host.conf File
The DNS Database Files
Caching-only named Configuration
Writing the Master Files
Verifying the Name Server Setup
Other Useful Tools

7. Serial Line IP

General Requirements

SLIP Operation

Dealing with Private IP Networks

Using dip

A Sample Script
A dip Reference

Running in Server Mode

8. The Point-to-Point Protocol

PPP on Linux

Running pppd

Using Options Files

Using chat to Automate Dialing

IP Configuration Options

Choosing IP Addresses
Routing Through a PPP Link

Link Control Options

General Security Considerations

Authentication with PPP

PAP Versus CHAP
The CHAP Secrets File
The PAP Secrets File

Debugging Your PPP Setup

More Advanced PPP Configurations

PPP Server
Demand Dialing
Persistent Dialing

9. TCP/IP Firewall

Methods of Attack

What Is a Firewall?

What Is IP Filtering?

Setting Up Linux for Firewalling

Kernel Configured with IP Firewall
The ipfwadm Utility
The ipchains Utility
The iptables Utility

Three Ways We Can Do Filtering

Original IP Firewall (2.0 Kernels)

Using ipfwadm
A More Complex Example
Summary of ipfwadm Arguments

IP Firewall Chains (2.2 Kernels)

Using ipchains
ipchains Command Syntax
Our Na�ve Example Revisited
Listing Our Rules with ipchains
Making Good Use of Chains

Netfilter and IP Tables (2.4 Kernels)

Backward Compatability with ipfwadmand ipchains
Using iptables
Our Na�ve Example Revisited, Yet Again

TOS Bit Manipulation

Setting the TOS Bits Using ipfwadm or ipchains
Setting the TOS Bits Using iptables

Testing a Firewall Configuration

A Sample Firewall Configuration

10. IP Accounting

Configuring the Kernel for IP Accounting

Configuring IP Accounting

Accounting by Address
Accounting by Service Port
Accounting of ICMP Datagrams
Accounting by Protocol

Using IP Accounting Results

Listing Accounting Data with ipfwadm
Listing Accounting Data with ipchains
Listing Accounting Data with iptables

Resetting the Counters

Flushing the Ruleset

Passive Collection of Accounting Data

11. IP Masquerade and Network Address Translation

Side Effects and Fringe Benefits

Configuring the Kernel for IP Masquerade

Configuring IP Masquerade

Setting Timing Parameters for IP Masquerade

Handling Name Server Lookups

More About Network Address Translation

12. ImportantNetwork Features

The inetd Super Server

The tcpd Access Control Facility

The Services and Protocols Files

Remote Procedure Call

Configuring Remote Loginand Execution

Disabling the r; Commands
Installing and Configuring ssh

13. The Network Information System

Getting Acquainted with NIS
NIS Versus NIS+
The Client Side of NIS
Running an NIS Server
NIS Server Security
Setting Up an NIS Client with GNU libc
Choosing the Right Maps
Using the passwd and group Maps
Using NIS with Shadow Support

14. The NetworkFile System

Preparing NFS
Mounting an NFS Volume
The NFS Daemons
The exports File
Kernel-Based NFSv2 Server Support
Kernel-Based NFSv3 Server Support

15. IPX and the NCP Filesystem

Xerox, Novell, and History

IPX and Linux

Caldera Support
More on NDS Support

Configuring the Kernel for IPXand NCPFS

Configuring IPX Interfaces

Network Devices Supporting IPX
IPX Interface Configuration Tools
The ipx_configure Command
The ipx_interface Command

Configuring an IPX Router

Static IPX Routing Using the ipx_route Command
Internal IPX Networks and Routing

Mounting a Remote NetWare Volume

A Simple ncpmount Example
The ncpmount Command in Detail
Hiding Your NetWare Login Password
A More Complex ncpmount Example

Exploring Some of the Other IPX Tools

Server List
Send Messages to NetWare Users
Browsing and Manipulating Bindery Data

Printing to a NetWare Print Queue

Using nprint with the Line Printer Daemon
Managing Print Queues

NetWare Server Emulation

16. ManagingTaylor UUCP

UUCP Transfers and Remote Execution

The Inner Workings of uucico
uucico Command-line Options

UUCP Configuration Files

A Gentle Introduction to Taylor UUCP
What UUCP Needs to Know
Site Naming
Taylor Configuration Files
General Configuration Options Using the config File
How to Tell UUCP About Other Systems Using the sys File
Identifying Available Devices Through the port File
How to Dial a Number Using the dial File
UUCP Over TCP
Using a Direct Connection

Controlling Access to UUCP Features

Command Execution
File Transfers
Forwarding

Setting Up Your System for Dialing In

Providing UUCP Accounts
Protecting Yourself Against Swindlers
Be Paranoid: Call Sequence Checks
Anonymous UUCP

UUCP Low-Level Protocols

Protocol Overview
Tuning the Transmission Protocol
Selecting Specific Protocols

Troubleshooting

uucico Keeps Saying “Wrong Time to Call”
uucico Complains That the Site Is Already Locked
You Can Connect to the Remote Site, but the Chat Script Fails
Your Modem Does Not Dial
Your Modem Tries to Dial but Doesn't Get Out
Login Succeeds, but the Handshake Fails

Log Files and Debugging

17. Electronic Mail

What Is a Mail Message?

How Is Mail Delivered?

Email Addresses

RFC-822
Obsolete Mail Formats
Mixing Different Mail Formats

How Does Mail Routing Work?

Mail Routing on the Internet
Mail Routing in the UUCP World
Mixing UUCP and RFC-822

Configuring elm

Global elm Options
National Character Sets

18. Sendmail

Introduction to sendmail

Installing sendmail

Overview of Configuration Files

The sendmail.cf and sendmail.mc Files

Two Example sendmail.mc Files
Typically Used sendmail.mc Parameters

Generating the sendmail.cf File

Interpreting and Writing Rewrite Rules

sendmail.cf R and S Commands
Some Useful Macro Definitions
The Lefthand Side
The Righthand Side
A Simple Rule Pattern Example
Ruleset Semantics

Configuring sendmail Options

Some Useful sendmail Configurations

Trusting Users to Set the From: Field
Managing Mail Aliases
Using a Smart Host
Managing Unwanted or Unsolicited Mail (Spam)
Configuring Virtual Email Hosting

Testing Your Configuration

Running sendmail

Tips and Tricks

Managing the Mail Spool
Forcing a Remote Host to Process its Mail Queue
Analyzing Mail Statistics

19. Getting EximUp and Running

Running Exim

If Your Mail Doesn't Get Through

Compiling Exim

Mail Delivery Modes

Miscellaneous config Options

Message Routing and Delivery

Routing Messages
Delivering Messages to Local Addresses
Alias Files
Mailing Lists

Protecting Against Mail Spam

UUCP Setup

20. Netnews

Usenet History
What Is Usenet, Anyway?
How Does Usenet Handle News?

21. C News

Miscellaneous Files

Control Messages

The cancel Message
newgroup and rmgroup
The checkgroups Message
sendsys, version, and senduuname

C News in an NFS Environment

Maintenance Tools and Tasks

22. NNTP and thenntpd Daemon

The NNTP Protocol

Connecting to the News Server
Pushing a News Article onto a Server
Changing to NNRP Reader Mode
Listing Available Groups
Listing Active Groups
Posting an Article
Listing New Articles
Selecting a Group on Which to Operate
Listing Articles in a Group
Retrieving an Article Header Only
Retrieving an Article Body Only
Reading an Article from a Group

Installing the NNTP Server

Restricting NNTP Access

NNTP Authorization

nntpd Interaction with C News

23. Internet News

Some INN Internals

Newsreaders and INN

Installing INN

Configuring INN: the Basic Setup

INN Configuration Files

Global Parameters
Configuring Newsgroups
Configuring Newsfeeds
Controlling Newsreader Access
Expiring News Articles
Handling Control Messages

Running INN

Managing INN: The ctlinnd Command

Add a New Group
Change a Group
Remove a Group
Renumber a Group
Allow/Disallow Newsreaders
Reject Newsfeed Connections
Allow Newsfeed Connections
Disable News Server
Restart News Server
Display Status of a Newsfeed
Drop a Newsfeed
Begin a Newsfeed
Cancel an Article

24. Newsreader Configuration

tin Configuration
trn Configuration
nn Configuration

A. Example Network:The Virtual Brewery

Connecting the Virtual Subsidiary Network

B. Useful Cable Configurations

A PLIP Parallel Cable
A Serial NULL Modem Cable

C. Linux Network Administrator's Guide, Second Edition Copyright Information

0. Preamble
1. Applicability and Definitions
2. Verbatim Copying
3. Copying in Quantity
4. Modifications
5. Combining Documents
6. Collections of Documents
7. Aggregation with Independent Works
8. Translation
9. Termination
10. Future Revisions of this License

D. SAGE: The SystemAdministrators Guild