CCNA 1 and 2 Companion Guide, - Cisco

1102.book Page i Tuesday, May 20, 2003 2:53 PM

Cisco Networking Academy Program

CCNA 1 and 2 Companion Guide
Third Edition

Cisco Systems, Inc.
Cisco Networking Academy Program

Cisco Press
201 West 103rd Street
Indianapolis, Indiana 46290 USA
www.ciscopress.com


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ii

Cisco Networking Academy Program

CCNA 1 and 2 Companion Guide
Third Edition
Cisco Systems, Inc.
Cisco Networking Academy Program
Copyright © 2003 Cisco Systems, Inc.
Published by:
Cisco Press
201 West 103rd Street
Indianapolis, IN 46290 USA

All rights reserved. No part of this book may be reproduced or transmitted in any form or by
any means, electronic or mechanical, including photocopying, recording, or by any information
storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review.
Printed in the United States of America 1 2 3 4 5 6 7 8 9 0
Library of Congress Cataloging-in-Publication Number: 2002116787
ISBN: 1-58713-110-2
First Printing June 2003

Trademark Acknowledgments
All terms mentioned in this book that are known to be trademarks or service marks have been
appropriately capitalized. Cisco Press or Cisco Systems, Inc., cannot attest to the accuracy of this
information. Use of a term in this book should not be regarded as affecting the validity of any
trademark or service mark.

Warning and Disclaimer
This book is designed to provide information about CCNA 1: Networking Basics and CCNA 2:
Routers and Routing Basics of the Cisco Networking Academy Program CCNA course. Every
effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied.
The information is provided on an “as is” basis. The author, Cisco Press, and Cisco Systems,
Inc., shall have neither liability nor responsibility to any person or entity with respect to any loss
or damages arising from the information contained in this book or from the use of the discs or
programs that may accompany it.
The opinions expressed in this book belong to the author and are not necessarily those of Cisco
Systems, Inc.

This book is part of the Cisco Networking Academy® Program series from Cisco Press. The
products in this series support and complement the Cisco Networking Academy Program
curriculum. If you are using this book outside the Networking Academy program, then you are
not preparing with a Cisco trained and authorized Networking Academy provider.
For information on the Cisco Networking Academy Program or to locate a Networking Academy,

please visit www.cisco.com/edu.


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iii

Feedback Information
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iv

Publisher

John Wait

Editor-in-Chief

John Kane

Executive Editor

Carl Lindholm

Cisco Representative

Anthony Wolfenden

Cisco Press Program Manager

Sonia Torres Chavez

Manager, Marketing Communications,
Cisco Systems

Scott Miller

Cisco Marketing Program Manager

Edie Quiroz

Production Manager

Patrick Kanouse

Senior Development Editor

Chris Cleveland

Senior Editor

Sheri Cain

Copy Editors

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Technical Editors

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Assistant Editor

Sarah Kimberly

Designer

Louisa Adair

Composition

Octal Publishing, Inc.

Indexer

Tim Wright


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Overview
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxv
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxvii
Part I

CCNA 1: Networking Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Chapter 1

Introduction to Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Chapter 2

Networking Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Chapter 3

Networking Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

Chapter 4

Cable Testing and Cabling LANs and WANs . . . . . . . . . . . . . . . 183

Chapter 5

Ethernet Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

Chapter 6

Ethernet Technologies and Ethernet Switching. . . . . . . . . . . . . 315

Chapter 7

TCP/IP Protocol Suite and IP Addressing . . . . . . . . . . . . . . . . . . 375

Chapter 8

Routing Fundamentals and Subnets . . . . . . . . . . . . . . . . . . . . . 427

Chapter 9

TCP/IP Transport and Application Layer. . . . . . . . . . . . . . . . . . . 477

Part II

CCNA 2: Routers and Routing Basics. . . . . . . . . . . . . . . . . . . . . 509

Chapter 10

WANs and Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511

Chapter 11

Router Fundamentals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553

Chapter 12

Router Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587

Chapter 13

Learning About Neighboring and Remote Devices. . . . . . . . . . 621

Chapter 14

Managing Cisco IOS Software . . . . . . . . . . . . . . . . . . . . . . . . . . 645

Chapter 15

Routing and Routing Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . 675

Chapter 16

Distance Vector Routing Protocols . . . . . . . . . . . . . . . . . . . . . . . 711

Chapter 17

TCP/IP Error and Control Messages . . . . . . . . . . . . . . . . . . . . . . 761


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Chapter 18

Basic Router Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . .787

Chapter 19

Intermediate TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .815

Chapter 20

Access Control Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .841

Part III

Appendixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .877

Appendix A Structured Cabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .879
Appendix B Glossary of Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .979
Appendix C Check Your Understanding Answer Key. . . . . . . . . . . . . . . . . .1009
Index

1047


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Table of Contents
Foreword
Introduction

xxv
xxvii

Part I

CCNA 1: Networking Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Chapter 1

Introduction to Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
The Fundamentals of Internet Connectivity . . . . . . . . . . . . . . . . . 5
PC Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electronic Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
PC Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Motherboard Components . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Desktop Versus Laptop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Network Interface Cards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
NIC and Modem Installation. . . . . . . . . . . . . . . . . . . . . . . . . . 13
Overview of High-Speed and Dialup Connectivity . . . . . . . . . . . 14
TCP/IP Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Testing Connectivity with Ping . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Web Browsers and Plug-Ins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Other Common Computer Applications . . . . . . . . . . . . . . . . . . . 18
Binary Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Binary Representation of Data. . . . . . . . . . . . . . . . . . . . . . . . . 19
Bits, Bytes, and Measurement Terms . . . . . . . . . . . . . . . . . . . . . . 19
Base 10 Number System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Base 2 Number System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Base 16 Number System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Decimal-to-Binary Conversion. . . . . . . . . . . . . . . . . . . . . . . . . 24
Binary-to-Decimal Conversion. . . . . . . . . . . . . . . . . . . . . . . . . 26
Hexadecimal and Binary Conversion . . . . . . . . . . . . . . . . . . . . 28

Four-Octet Dotted-Decimal Representation of a 32-Bit Binary
Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Boolean Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
IP Addresses and Subnet Masks . . . . . . . . . . . . . . . . . . . . . . . . 32
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39


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Chapter 2

Networking Fundamentals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Networking Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Data Networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Computer Networking History . . . . . . . . . . . . . . . . . . . . . . . .47
Network Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
Local-Area Networks (LANs) . . . . . . . . . . . . . . . . . . . . . . . . .49
Wide-Area Networks (WANs) . . . . . . . . . . . . . . . . . . . . . . . . .50
Metropolitan-Area Networks (MANs). . . . . . . . . . . . . . . . . . .52
Specialized Networks Located Within the LAN . . . . . . . . . . . .53
Virtual Private Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
Digital Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
The Importance of Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . .58
Analogies That Describe Digital Bandwidth . . . . . . . . . . . . . . . .59
Digital Bandwidth Measurements . . . . . . . . . . . . . . . . . . . . . .61
Bandwidth Limitations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Data Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
Data Transfer Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
Digital Bandwidth Versus Analog Bandwidth. . . . . . . . . . . . . .66
Networking Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
Using Layers to Analyze Problems in a Flow of Materials . . . .67
Using Layers to Describe Data Communication . . . . . . . . . . . .68
The OSI Reference Model . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
OSI Layers and Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
Peer-to-Peer Communications . . . . . . . . . . . . . . . . . . . . . . . . .72
DoD (TCP/IP) Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74
Detailed Encapsulation Process . . . . . . . . . . . . . . . . . . . . . . . .75
Networking Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78
Repeaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79
Hubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79
Network Interface Cards . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81
Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Layer 2 Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84
Voice, DSL, Cable Modem, and Optical Devices . . . . . . . . . . .86
Security Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89
Wireless Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91
Network Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93
Bus Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95
Star and Extended-Star Topologies. . . . . . . . . . . . . . . . . . . . . .95
Ring Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97


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Hierarchical Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Full-Mesh and Partial-Mesh Topologies. . . . . . . . . . . . . . . . . . 98
Logical Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Chapter 3

Networking Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Electricity Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Atoms and Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Electrical Properties of Matter . . . . . . . . . . . . . . . . . . . . . . . . 117
Measuring Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Wattage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Resistance and Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Copper Media. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
American Wire Gauge System . . . . . . . . . . . . . . . . . . . . . . . . 123
Twisted-Pair Cable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Shielded Twisted-Pair Cable. . . . . . . . . . . . . . . . . . . . . . . . . . 124
Unshielded Twisted-Pair Cable. . . . . . . . . . . . . . . . . . . . . . . . 125
Coaxial Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Cable Specification and Termination . . . . . . . . . . . . . . . . . . . 130
Optical Media. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
The Electromagnetic Spectrum. . . . . . . . . . . . . . . . . . . . . . . . 134
The Ray Model of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
The Law of Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

The Law of Refraction (Snell’s Law) . . . . . . . . . . . . . . . . . . . 138
Total Internal Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Fiber-Optic Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Multimode Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Single-Mode Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Cable Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Other Optical Networking Components . . . . . . . . . . . . . . . . 147
Signals and Noise in Optical Fiber . . . . . . . . . . . . . . . . . . . . . 149
Installation, Care, and Testing of Optical Fiber . . . . . . . . . . . 151
Wireless Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Wireless Data Communications . . . . . . . . . . . . . . . . . . . . . . . 154


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Wireless Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
Radio Frequency Bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
Spread-Spectrum Technology . . . . . . . . . . . . . . . . . . . . . . . . .159
FHSS Versus DSSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159
Wireless Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161
Wireless LAN Organization and Standards . . . . . . . . . . . . . .161
Wireless Devices and Topologies . . . . . . . . . . . . . . . . . . . . . .162
How Wireless LANs Communicate . . . . . . . . . . . . . . . . . . . .165
Authentication and Association . . . . . . . . . . . . . . . . . . . . . . .166
The Radio Wave/Microwave Spectrum. . . . . . . . . . . . . . . . . .168
Signals and Noise on a WLAN. . . . . . . . . . . . . . . . . . . . . . . .169
Wireless Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
WEP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

VPN, EAP, and LEAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . .176
Chapter 4

Cable Testing and Cabling LANs and WANs . . . . . . . . . . . . . . .183
Background for Studying Frequency-Based Cable Testing . . . . .184
Waves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184
Sine Waves and Square Waves . . . . . . . . . . . . . . . . . . . . . . . .185
Exponents and Logarithms. . . . . . . . . . . . . . . . . . . . . . . . . . .186
Decibels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187
Viewing Signals in Time and Frequency. . . . . . . . . . . . . . . . . . .188
Noise in Time and Frequency . . . . . . . . . . . . . . . . . . . . . . . . . .189
Analog and Digital Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . .190
Signals and Noise on Networking Media . . . . . . . . . . . . . . . . .191
Signaling over Copper and Fiber-Optic Cabling . . . . . . . . . . .192
Attenuation and Insertion Loss on Copper Media . . . . . . . . .195
Source of Noise on Copper Media . . . . . . . . . . . . . . . . . . . . .196
Cable Testing Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199
Other Test Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .202
Time-Based Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . .202
Testing Fiber-Optic Cables . . . . . . . . . . . . . . . . . . . . . . . . . . .203
A New Cabling Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . .204
Cabling the LANs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205
LAN Physical Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205


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Ethernet in the Campus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
Ethernet Media and Connector Requirement. . . . . . . . . . . . . 208
Connection Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
UTP Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
LAN Connection Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
Repeaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
Hubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Bridges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Wireless Networking Media . . . . . . . . . . . . . . . . . . . . . . . . . 222
Host LAN Connectivity: NICs and Interfaces . . . . . . . . . . . . 225
Workstation and Server Relationships. . . . . . . . . . . . . . . . . . . . 226
Peer-to-Peer Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Client/Server Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Cabling the WAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
WAN Physical Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
WAN Serial Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
Routers and Serial Connections . . . . . . . . . . . . . . . . . . . . . . . 234
Routers and ISDN BRI Connections . . . . . . . . . . . . . . . . . . . 236
Routers and DSL Connections . . . . . . . . . . . . . . . . . . . . . . . . 238
Routers and Cable Connections. . . . . . . . . . . . . . . . . . . . . . . 239
Setting Up Console Connections . . . . . . . . . . . . . . . . . . . . . . 240
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
Chapter 5

Ethernet Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

History and Evolution of Ethernet . . . . . . . . . . . . . . . . . . . . . . 251
Introduction to Ethernet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
IEEE Ethernet Naming Rules . . . . . . . . . . . . . . . . . . . . . . . . . 253
IEEE 802.3/Ethernet and the OSI Model . . . . . . . . . . . . . . . . 255
MAC Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
Framing in General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Ethernet Frame Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
Ethernet Frame Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
Ethernet Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Media Access Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Ethernet MAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
Simplex, Half-Duplex, and Full-Duplex Operation . . . . . . . . 271


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Ethernet Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272
Interframe Spacing and Backoff . . . . . . . . . . . . . . . . . . . . . . .275
Error Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .277
Types of Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .279
Ethernet Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282
Ethernet Autonegotiation . . . . . . . . . . . . . . . . . . . . . . . . . . . .285
Link Establishment and Full/Half Duplex . . . . . . . . . . . . . . .288
Collision Domains and Broadcast Domains. . . . . . . . . . . . . . . .290
Directly Connected Networks . . . . . . . . . . . . . . . . . . . . . . . .290
Indirectly Connected Networks . . . . . . . . . . . . . . . . . . . . . . .291
Collisions and Collision Domains . . . . . . . . . . . . . . . . . . . . .292
Segmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .295

Layer 2 Broadcasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .297
Broadcast Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .300
Introduction to Data Flow . . . . . . . . . . . . . . . . . . . . . . . . . . .300
Network Segment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .304
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .306
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . .309
Chapter 6

Ethernet Technologies and Ethernet Switching . . . . . . . . . . . . .315
10-Mbps and 100-Mbps Ethernet . . . . . . . . . . . . . . . . . . . . . . .315
10-Mbps Versions of Ethernet . . . . . . . . . . . . . . . . . . . . . . . .316
10BASE5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .320
10BASE2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .321
10BASE-T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .322
10BASE-T Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . .326
100BASE-TX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .329
100BASE-FX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .332
Fast Ethernet Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . .334
Gigabit, 10-Gb, and Future Ethernet . . . . . . . . . . . . . . . . . . . . .337
1000-Mbps Versions of Ethernet (Gigabit) . . . . . . . . . . . . . . .337
1000BASE-T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .339
1000BASE-SX and 1000BASE-LX . . . . . . . . . . . . . . . . . . . . .342
Gigabit Ethernet Architecture. . . . . . . . . . . . . . . . . . . . . . . . .345
10-Gbps Versions of Ethernet. . . . . . . . . . . . . . . . . . . . . . . . .347
10GbE Media, Connections, and Architecture . . . . . . . . . . . .350
The Future of Ethernet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .354
Ethernet Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .355

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Layer 2 Bridging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
Layer 2 Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
Microsegmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
Full-Duplex Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
Switch Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
Introduction to the Spanning Tree Protocol . . . . . . . . . . . . . . 362
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
Chapter 7

TCP/IP Protocol Suite and IP Addressing . . . . . . . . . . . . . . . . . . 375
Introduction to TCP/IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
Application Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
Transport Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
Internet Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
Network Access Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
Comparing the OSI Reference Model Layers
and the TCP/IP Reference Model Layers . . . . . . . . . . . . . . . 382
Internet Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383
IP Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
32-Bit Dotted-Decimal IP Address . . . . . . . . . . . . . . . . . . . . . 386
Decimal and Binary Conversion. . . . . . . . . . . . . . . . . . . . . . . 389
IPv4 Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
IP Address Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394

Reserved IP Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
Public and Private Addresses . . . . . . . . . . . . . . . . . . . . . . . . . 400
Introduction to Subnetting. . . . . . . . . . . . . . . . . . . . . . . . . . . 402
IPv4 Versus IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
IP Address Assignment, Acquisition, and Hierarchy . . . . . . . . . 407
Obtaining an Internet Address . . . . . . . . . . . . . . . . . . . . . . . . 407
Static Assignment of an IP Address . . . . . . . . . . . . . . . . . . . . 408
Address Resolution Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 408
RARP IP Address Assignment . . . . . . . . . . . . . . . . . . . . . . . . 412
Bootstrap Protocol (BOOTP) IP Address Assignment . . . . . . 414
Dynamic Host Configuration Protocol (DHCP)
IP Address Assignment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
Problems in Address Resolution. . . . . . . . . . . . . . . . . . . . . . . 417
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419


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Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .421
Review Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .422
Chapter 8

Routing Fundamentals and Subnets. . . . . . . . . . . . . . . . . . . . . .427
Routed, Routable, and Routing Protocols . . . . . . . . . . . . . . . . .427
Routing Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .430
Routing Versus Switching. . . . . . . . . . . . . . . . . . . . . . . . . . . .432
Routed Versus Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .435
Path Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .437

Routing Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .440
Routing Algorithms and Metrics . . . . . . . . . . . . . . . . . . . . . .441
Interior and Exterior Routing Protocols . . . . . . . . . . . . . . . . .443
Routing Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .444
IP as a Routed Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . .448
Packet Propagation and Switching Within a Router . . . . . . . .449
Connectionless Versus Connection-Oriented
Network Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .451
Anatomy of an IP Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . .453
The Mechanics of Subnetting . . . . . . . . . . . . . . . . . . . . . . . . . .455
Introduction to and Reasons for Subnetting . . . . . . . . . . . . . .455
Establishing the Subnet Mask Address . . . . . . . . . . . . . . . . . .458
Creating a Subnet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .460
Calculating the Resident Subnetwork Through ANDing . . . .463
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .465
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .467
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . .470

Chapter 9

TCP/IP Transport and Application Layer . . . . . . . . . . . . . . . . . . .477
Understanding the TCP/IP Transport Layer . . . . . . . . . . . . . . . .478
Flow Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .479
Session Establishment, Maintenance, and Termination
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .480
Three-Way Handshake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .482
Windowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .484
TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .486
UDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .487

TCP and UDP Port Numbers . . . . . . . . . . . . . . . . . . . . . . . . .488
TCP/IP Application Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491


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Introduction to the Application Layer . . . . . . . . . . . . . . . . . . 491
DNS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
FTP and TFTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
HTTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496
SMTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
SNMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
Telnet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
Part II

CCNA 2: Routers and Routing Basics. . . . . . . . . . . . . . . . . . . . . 509

Chapter 10

WANs and Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
WAN Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
WAN Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
WAN Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
WAN Connection Options. . . . . . . . . . . . . . . . . . . . . . . . . . . 519
WAN Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529

Router Internal Components . . . . . . . . . . . . . . . . . . . . . . . . . 529
Router External Connections. . . . . . . . . . . . . . . . . . . . . . . . . 535
Management Port Connections . . . . . . . . . . . . . . . . . . . . . . . 535
The Function of a Router in a WAN . . . . . . . . . . . . . . . . . . . 536
Lab WAN Simulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546

Chapter 11

Router Fundamentals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
Router Boot Sequence and Setup Mode . . . . . . . . . . . . . . . . . . 553
Router Startup Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
System Configuration Dialog . . . . . . . . . . . . . . . . . . . . . . . . . 555
Setting Up Global Parameters . . . . . . . . . . . . . . . . . . . . . . . . 556
Router LED Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
Initial Router Boot-Up Output. . . . . . . . . . . . . . . . . . . . . . . . 560
Establishing a HyperTerminal Session . . . . . . . . . . . . . . . . . . . . 562
Logging into the Router . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
Keyboard Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566
Router Help Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569


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Cisco IOS Software Editing Commands . . . . . . . . . . . . . . . . . .571
Router Command History. . . . . . . . . . . . . . . . . . . . . . . . . . . . .572

Cisco IOS Software Fundamentals. . . . . . . . . . . . . . . . . . . . . . .574
Operation of Cisco IOS Software . . . . . . . . . . . . . . . . . . . . . .574
Cisco IOS Software Features . . . . . . . . . . . . . . . . . . . . . . . . .575
The show version Command . . . . . . . . . . . . . . . . . . . . . . . . .577
Router User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .577
Router User Interface and Modes. . . . . . . . . . . . . . . . . . . . . .578
Troubleshooting Cisco IOS Software . . . . . . . . . . . . . . . . . . . . .579
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .581
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .582
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . .582
Chapter 12

Router Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .587
Command-Line Interface Command Modes . . . . . . . . . . . . . . .587
User Command List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .587
Privileged Mode Command List . . . . . . . . . . . . . . . . . . . . . . .589
Router Configuration Modes . . . . . . . . . . . . . . . . . . . . . . . . .592
Router Startup Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .594
Configuring a Router Name . . . . . . . . . . . . . . . . . . . . . . . . . . .595
Configuring and Protecting Router Passwords. . . . . . . . . . . . . .596
Examining the show Commands . . . . . . . . . . . . . . . . . . . . . . . .597
Configuring a Serial Interface . . . . . . . . . . . . . . . . . . . . . . . . . .600
Configuring an Ethernet Interface . . . . . . . . . . . . . . . . . . . . . . .601
Executing Changes to the Router . . . . . . . . . . . . . . . . . . . . . . .602
Finishing the Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . .603
Importance of Configuration Standards . . . . . . . . . . . . . . . . .603
Providing Interface Descriptions. . . . . . . . . . . . . . . . . . . . . . .604
Configuring Interface Descriptions . . . . . . . . . . . . . . . . . . . . .604
Login Banners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .605
Configuring a Message of the Day . . . . . . . . . . . . . . . . . . . . .606

Host Name Resolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .606
Configuration Backup and Documentation . . . . . . . . . . . . . .607
Password Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .609
Overview of Password Recovery . . . . . . . . . . . . . . . . . . . . . .609
Password Recovery Technique 1. . . . . . . . . . . . . . . . . . . . . . .610
Password Recovery Technique 2. . . . . . . . . . . . . . . . . . . . . . .611


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Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615
Chapter 13

Learning About Neighboring and Remote Devices. . . . . . . . . . 621
Introduction to CDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
Obtaining Information with CDP . . . . . . . . . . . . . . . . . . . . . 622
Showing CDP Neighbors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623
Implementating, Monitoring, and Maintaining
CDP Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625
Creating a Network Map of the Environment . . . . . . . . . . . . 627
Disabling and Troubleshooting CDP . . . . . . . . . . . . . . . . . . . 627
Getting Information About Remote Devices . . . . . . . . . . . . . . . 629
Telnet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629
Alternative Connectivity Tests . . . . . . . . . . . . . . . . . . . . . . . . 632
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 640
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641

Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641

Chapter 14

Managing Cisco IOS Software . . . . . . . . . . . . . . . . . . . . . . . . . . 645
Stages of the Router Power-On/Boot Sequence . . . . . . . . . . . . . 645
Locating and Loading Cisco IOS Software . . . . . . . . . . . . . . . . 646
Using the boot system Command. . . . . . . . . . . . . . . . . . . . . . 647
Configuration Register Values . . . . . . . . . . . . . . . . . . . . . . . . 649
Displaying the Currently Running Cisco IOS Software
Version. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
Managing Cisco IOS Software Images . . . . . . . . . . . . . . . . . . . 651
Cisco IOS Software Naming Conventions . . . . . . . . . . . . . . . 654
Managing Configuration File Using TFTP . . . . . . . . . . . . . . . 656
Managing Configuration Files with HyperTerminal . . . . . . . . 658
Managing Cisco IOS Software Images with TFTP . . . . . . . . . 660
Managing Cisco IOS Software Images with ROMmon . . . . . 662
Verifying the File System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670


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xviii

Chapter 15

Routing and Routing Protocols . . . . . . . . . . . . . . . . . . . . . . . . . .675

Routing Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .675
How Routers Route Packets from Source to Destination . . . .676
Network and Host Addressing . . . . . . . . . . . . . . . . . . . . . . . .677
Path Selection and Packet Switching. . . . . . . . . . . . . . . . . . . .678
Routed Protocols Versus Routing Protocols . . . . . . . . . . . . . .678
Network Layer Protocol Operations . . . . . . . . . . . . . . . . . . .679
Multiprotocol Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .680
Static Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .681
Static Versus Dynamic Routes . . . . . . . . . . . . . . . . . . . . . . . .681
The Purpose of a Static Route . . . . . . . . . . . . . . . . . . . . . . . .681
Static Route Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .681
Configuring Static Routes. . . . . . . . . . . . . . . . . . . . . . . . . . . .684
How a Default Route Is Used. . . . . . . . . . . . . . . . . . . . . . . . .687
Configuring Default Route Forwarding . . . . . . . . . . . . . . . . .687
Verifying Static Route Configuration . . . . . . . . . . . . . . . . . . .689
Troubleshooting Static Route Configuration . . . . . . . . . . . . .689
Dynamic Routing Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .690
Routing Protocol Examples . . . . . . . . . . . . . . . . . . . . . . . . . .691
Purpose of a Routing Protocol and Autonomous Systems . . .692
Dynamic Routing Operations. . . . . . . . . . . . . . . . . . . . . . . . .693
How Distances on Network Paths Are Determined by
Various Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .693
Identifying the Classes of Routing Protocols . . . . . . . . . . . . . . .694
Distance Vector Routing Protocol Features . . . . . . . . . . . . . .695
Link-State Routing Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . .697
Hybrid Routing Protocol Features . . . . . . . . . . . . . . . . . . . . .701
Configuring a Router to Use Routing Protocols. . . . . . . . . . . . .701
Autonomous Systems and IGP vs. EGP . . . . . . . . . . . . . . . . . . .703
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .704
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .705

Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . .706

Chapter 16

Distance Vector Routing Protocols . . . . . . . . . . . . . . . . . . . . . . .711
Initial Router Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . .711
Distance Vector Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .712
Maintaining Routing Information Through Distance
Vector Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .712


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xix

Load Balancing Across Multiple Paths. . . . . . . . . . . . . . . . . . 713
How Routing Loops Occur in Distance Vector . . . . . . . . . . . 714
Defining a Maximum to Prevent Count to Infinity. . . . . . . . . 715
Eliminating Routing Loops Through Split Horizon . . . . . . . . 716
Route Poisoning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
Avoiding Routing Loops with Triggered Updates. . . . . . . . . . 718
Preventing Routing Loops with Hold-Down Timers . . . . . . . 719
Preventing Routing Updates Through an Interface. . . . . . . . . 720
Examining the Routing Table . . . . . . . . . . . . . . . . . . . . . . . . . . 721
The show ip route Command . . . . . . . . . . . . . . . . . . . . . . . . 721
Determining the Gateway of Last Resort . . . . . . . . . . . . . . . . 722
Determining Route Source to Route Destination . . . . . . . . . . 723
Determining Layer 2 and Layer 3 Addresses from the Source to the
Destination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723
Determining Route Administrative Distance . . . . . . . . . . . . . 724

Determining Route Metric . . . . . . . . . . . . . . . . . . . . . . . . . . . 725
Determining Route Next Hop . . . . . . . . . . . . . . . . . . . . . . . . 726
Determining Last Route Updates . . . . . . . . . . . . . . . . . . . . . . 726
Observing Multiple Paths to Destination . . . . . . . . . . . . . . . . 729
RIP Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729
Enabling RIP on an IP Network. . . . . . . . . . . . . . . . . . . . . . . 730
Using the ip classless Command. . . . . . . . . . . . . . . . . . . . . . . 731
Common RIP Configuration Issues . . . . . . . . . . . . . . . . . . . . 732
Verifying RIP Configuration . . . . . . . . . . . . . . . . . . . . . . . . . 735
Troubleshooting RIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738
Load Balancing with RIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 740
Integrating Static Routes with RIP . . . . . . . . . . . . . . . . . . . . . 741
IGRP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744
IGRP Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744
IGRP Metrics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745
Interior, System, and Exterior IGRP Routes . . . . . . . . . . . . . . 746
IGRP Stability Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747
Configuring IGRP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 748
Verifying the IGRP Configuration . . . . . . . . . . . . . . . . . . . . . 749
Troubleshooting IGRP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 751
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756


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xx

Chapter 17

TCP/IP Error and Control Messages . . . . . . . . . . . . . . . . . . . . . .761
Functionality and Role of IP in Error Control . . . . . . . . . . . . . .761
ICMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .762
ICMP Message Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . .762
Error Reporting and Error Correction . . . . . . . . . . . . . . . . . .763
Unreachable Networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .764
Using ping to Test Destination Reachability . . . . . . . . . . . . . .765
Detecting Excessively Long Routes. . . . . . . . . . . . . . . . . . . . .769
ICMP Message Format: Echo Messages . . . . . . . . . . . . . . . . .769
ICMP Message Format: Destination Unreachable Message . .771
Miscellaneous Error Reporting. . . . . . . . . . . . . . . . . . . . . . . .773
TCP/IP Suite Control Messages . . . . . . . . . . . . . . . . . . . . . . . . .773
ICMP Redirect/Change Requests . . . . . . . . . . . . . . . . . . . . . .773
Clock Synchronization and Transit Time Estimation . . . . . . .775
Information Requests and Reply Message Formats . . . . . . . .776
Address Mask Requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . .777
Router-Discovery Message . . . . . . . . . . . . . . . . . . . . . . . . . . .778
Router-Solicitation Message . . . . . . . . . . . . . . . . . . . . . . . . . .780
Congestion and Flow-Control Messages . . . . . . . . . . . . . . . . . .780
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .781
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .782
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . .782

Chapter 18

Basic Router Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . .787
Introduction to Network Testing . . . . . . . . . . . . . . . . . . . . . . . .787
Structured Approach to Troubleshooting . . . . . . . . . . . . . . . .788
Testing by OSI Layers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .790

Troubleshooting Layer 1 Using Indicators . . . . . . . . . . . . . . .791
Troubleshooting Layer 2 Using the show interface
Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .792
Troubleshooting Layer 3 Using ping. . . . . . . . . . . . . . . . . . . .793
Troubleshooting Layer 3 Issues Using traceroute . . . . . . . . . .795
Troubleshooting Layer 7 Using Telnet . . . . . . . . . . . . . . . . . .797
Troubleshooting Router Issues Using the show interface
and show interfaces Commands . . . . . . . . . . . . . . . . . . . . . . .798
Troubleshooting Routing Issues Using the show cdp
neighbors Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .801
Troubleshooting Routing Issues Using show ip route and
show ip protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .803


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Troubleshooting Router Connections Using the show
controllers serial Command . . . . . . . . . . . . . . . . . . . . . . . . . . 805
Introduction to debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810
Chapter 19

Intermediate TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815
The TCP/IP Protocol Suite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815
TCP/IP Protocol Stack and the Application Layer . . . . . . . . . 816
TCP/IP Protocol Stack and the Transport Layer. . . . . . . . . . . 818

TCP and UDP Segment Format . . . . . . . . . . . . . . . . . . . . . . . 819
TCP Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820
Three-Way Handshake. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821
Denial-of-Service Attacks During Synchronization. . . . . . . . . 822
Windowing and Window Size . . . . . . . . . . . . . . . . . . . . . . . . 823
Sequencing Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825
Positive ACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
UDP Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827
Overview of Transport Layer Ports . . . . . . . . . . . . . . . . . . . . . . 828
Multiple Conversations Between Hosts . . . . . . . . . . . . . . . . . 828
Ports for Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
Ports for Clients. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832
Port Numbering and Well-Known Ports . . . . . . . . . . . . . . . . 832
Example of Multiple Sessions Between Hosts . . . . . . . . . . . . 832
Comparison of MAC Addresses, IP Addresses, and
Port Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833
TCP/IP and the Internet Layer. . . . . . . . . . . . . . . . . . . . . . . . . . 833
How ARP Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836

Chapter 20

Access Control Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
ACL Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
Why Create ACLs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
Creating an ACL: Why Order Matters . . . . . . . . . . . . . . . . . . . 844
Using ACLs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844

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How ACLs Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .845
ACL Configuration Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . .847
Assigning a Unique Number to Each ACL. . . . . . . . . . . . . . . . .847
Using Wildcard Mask Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . .848
Using the Wildcard any . . . . . . . . . . . . . . . . . . . . . . . . . . . . .850
Using the Wildcard host . . . . . . . . . . . . . . . . . . . . . . . . . . . . .851
Standard ACLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .852
Extended ACLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .855
Configuring Extended ACLs for ICMP. . . . . . . . . . . . . . . . . .861
Configuring Extended ACLs for IGMP . . . . . . . . . . . . . . . . .861
Configuring Extended ACLs for TCP . . . . . . . . . . . . . . . . . . .861
Configuring Extended ACLs for UDP. . . . . . . . . . . . . . . . . . .862
Extended ACL Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . .862
Named ACLs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .863
Placing ACLs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .866
Firewalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .867
Using ACLs with Firewalls . . . . . . . . . . . . . . . . . . . . . . . . . . .868
Restricting Virtual Terminal Access . . . . . . . . . . . . . . . . . . . . . .869
Verifying ACLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .870
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .871
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .872
Check Your Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . .872
Part III

Appendixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .877

Appendix A Structured Cabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .879
Mounting Jacks in Drywall . . . . . . . . . . . . . . . . . . . . . . . . . .928
Mounting Jacks in Plaster . . . . . . . . . . . . . . . . . . . . . . . . . . .929
Mounting Jacks in Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . .930
Flush-Mounting a Jack in a Wall . . . . . . . . . . . . . . . . . . . . . .930
Pulling Cable to the Jacks. . . . . . . . . . . . . . . . . . . . . . . . . . . .930
Fishing Cable from Below a Wall . . . . . . . . . . . . . . . . . . . . . .931
Appendix B Glossary of Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .979
Appendix C Check Your Understanding Answer Key. . . . . . . . . . . . . . . . . .1009
Index

1047


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xxiii

Cisco Systems Networking Icon Legend
Cisco Systems, Inc., uses a standardized set of icons to represent devices in network
topology illustrations. The following icon legend shows the most commonly used icons
that you might encounter throughout this book.

Hub

DSU/CSU
DSU/CSU

Multilayer

Switch

ATM
Switch

ISDN/Frame
Relay Switch

Gateway

Access
Server

Router

Bridge

Catalyst
Switch

Communication
Server

PC

PC with
Software

Sun
Workstation

Web
Server

Cisco Works
Workstation

Cluster
Controller

Macintosh

Modem
File
Server

Printer

Token
Ring
Token Ring

Line: Ethernet

Laptop

Terminal

Front End
Processor

IBM
Mainframe

FDDI

FDDI

Network Cloud

Line: Serial

Line: Switched Serial


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xxiv

Command Syntax Conventions
The conventions used to present command syntax in this book are the same conventions used in the Cisco IOS Software Command Reference. The Command Reference
describes these conventions as follows:
■

Vertical bars (|) separate alternative, mutually exclusive elements.

■

Square brackets ([ ]) indicate optional elements.

■

Braces ({ }) indicate a required choice.

■

Braces within brackets ([{ }]) indicate a required choice within an optional
element.

■

Boldface indicates commands and keywords that are entered exactly as shown.

■

Italic indicates arguments for which you supply values.


1102.book Page xxv Tuesday, May 20, 2003 2:53 PM

xxv

Foreword
Throughout the world, the Internet has brought tremendous new opportunities for
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