Cisco press cisco BGP 4 command and configuration handbook CCIE professional development may 2001 ISBN 1587055732

Cisco BGP-4 Command and Configuration Handbook is an exhaustive practical reference to the commands contained within BGP-4.. Access Registrar, AccessPath, Any to Any,AtmDirector, CCDA, C

associated with Internet service providers or enterprise networks that depend heavily on the Internet, a background in BGP-4 is

essential Moving beyond background

information, BGP contains a great number of commands, and practical information on

Cisco BGP-4 Command and Configuration

Handbook is an exhaustive practical reference

to the commands contained within BGP-4 For each command/subcommand, author Bill

Parkhurst explains the intended use or

function and how to properly configure it.

Then he presents scenarios to demonstrate every facet of the command and its use,

the practical side of BGP-4.

information storage and retrieval system, without written

permission from the publisher, except for the inclusion of briefquotations in a review

fitness is implied

The information is provided on an "as is" basis The author,Cisco Press, and Cisco Systems, Inc shall have neither liability

accompany it

The opinions expressed in this book belong to the author andare not necessarily those of Cisco Systems, Inc

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 tothe accuracy of this information Use of a term in this bookshould not be regarded as affecting the validity of any

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Credits

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Copyright © 2000 Cisco Systems, Inc All rights reserved

Printed in the USA Access Registrar, AccessPath, Any to Any,AtmDirector, CCDA, CCDE, CCDP, CCIE, CCNA, CCNP, CCSI, CD-PAC, the Cisco logo, Cisco Certified Internetwork Expert logo,

CiscoLink, the Cisco Management Connection logo, the Cisco

NetWorks logo, the Cisco Powered Network logo, Cisco Systems

Capital, the Cisco Systems Capital logo, Cisco Systems

Registrar, Packet, PIX, Point and Click Internetworking, Policy

Builder, Precept, RouteStream, Secure Script, ServiceWay,

SlideCast, SMARTnet, StreamView, The Cell, TrafficDirector,

TransPath, ViewRunner, VirtualStream, VisionWay, VlanDirector,Workgroup Director, and Workgroup Stack are trademarks;

Changing the Way We Work, Live, Play, and Learn, Empoweringthe Internet Generation, The Internet Economy, and The NewInternet Economy are service marks; and ASIST, BPX, Catalyst,Cisco, Cisco IOS, the Cisco IOS logo, Cisco Systems, the CiscoSystems logo, the Cisco Systems Cisco Press logo,

Enterprise/Solver, EtherChannel, EtherSwitch, FastHub,

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StrataView Plus, Stratm, TeleRouter, and VCO are registeredtrademarks of Cisco Systems, Inc and/or its affiliates in theU.S and certain other countries All other trademarks

mentioned in this document are the property of their respectiveowners The use of the word partner does not imply a

partnership relationship between Cisco and any of its resellers.(9908R)

Dedication

I would like to dedicate this book to all those who have beeninstrumental in my professional development and success

Without their help, guidance, and friendship my life would havetaken a less rewarding path There have been many individualswho have had a profound affect on my professional career buttwo stand out in my mind I want to thank Dr Everett L

Johnson, Chairman and Professor of Electrical and ComputerEngineering at Wichita State University for being my mentor,teacher, and friend Dr "J" made my twelve years at Wichita

State University rewarding and most importantly, fun Finally, Iwant to thank Dr Roy H Norris, Professor and Chair Emeritus ofWichita State University for opening the door and letting me in.

Laboratory

Bill Wagner works as a Cisco Certified Systems Instructor for

Mentor Technologies He has 22 years of computer

programming and data communication experience He hasworked for corporations and companies such as IndependentComputer Consultants, Numerax, McGraw-Hill, and Standardand Poors His teaching experience started with the ChubbInstitute, Protocol Interface, Inc., and Geotrain Currently heteaches at Mentor Technologies

Steve Wisniewski is a Systems Engineer for Fujitsu Network

Communications Steve has authored a book titled NetworkAdministration from Prentice Hall and has edited several otherCisco Press books Steve resides with his wife Ellen in EastBrunswick, New Jersey

Writing a book is never an easy endeavor Without the help andguidance of John Kane, Editor-In-Chief, and Christopher

Cleveland, Development Editor, of Cisco Press the task of

writing this book would have been less enjoyable John andChris may have cracked the whip occasionally but it was alwaysdone with diplomacy and humor I want to especially

acknowledge my wife Debbie for her constant encouragementand for the wonderful job she did in proofreading the

manuscript The number of required corrections was minimalthanks to her efforts and attention to detail Debbie made melook good in the eyes of my editor and for that I am thankful

I have been involved with the world of networking from manydirections My experiences in education, network consulting,service provider support, and certification have shown me thatthere is a common thread that frustrates people in all of thesearenas That common thread is documentation There are manyfactors that cause documentation to be frustrating but the mostcommon are amount, clarity, and completeness The amount ofdocumentation available, especially in regards to BGP, can beoverwhelming For a person who is beginning to learn BGP, thequestion is "where do I begin"? There are very good books,

RFCs, white papers, and command references available, but it isdifficult to know where to start The clarity of documentationdepends on your personal situation For a seasoned BGP

designer the documentation may be clear and concise To anindividual preparing for a professional certification such as theCCIE the same documentation may be confusing Even if thedocumentation is clear it is sometimes not complete You mayunderstand the words but be confused on the application Thepurpose of this book is to provide a BGP handbook that is clear,concise, and complete This book is not meant to be read fromcover to cover The way you use this book will depend on yourobjectives If you are preparing for the CCIE written and labexams then this book can be used as a laboratory guide to learnthe purpose and proper use of every BGP command If you are

a network designer then this book can be used as a ready

reference for any BGP command In order to satisfy these

varying audiences the structure of this book is reasonably

simple Each BGP command is illustrated using the followingstructure:

Listing of the command structure and syntax

The purpose of the command and the situation where thecommand is used

The first release of the IOS in which the command appeared

One or more configuration examples to demonstrate theproper use of the command

Procedures and examples to verify that the command isworking properly

How to troubleshoot the command when things are not

working as intended

The example scenarios that demonstrate the proper use of theBGP commands can be implemented on a minimum number ofrouters This will allow you to learn each command without

requiring an extensive and expensive lab configuration Thescenarios are presented so that the purpose and use of eachcommand can be presented without clouding the issue Some ofthe examples lead you into common non-working situations inorder to reinforce the understanding of the operation of the

particular BGP command

For those of you who will use this book as a tool for preparingfor the BGP component of the CCIE exam I would suggest thatyou read Appendix A, B, and C before diving into the variouscommand examples Appendix A is an overview of BGP

operation and concepts Appendix B is a review of regular

expressions and their use with BGP Appendix C covers the

structure, logic, and use of route maps Regular expressionsand route maps tend to be areas where candidates typically runinto trouble on the CCIE lab exam My hope is that this

handbook will help you prepare for the CCIE exam, allow you toproperly use BGP in your network, or both.

Throughout the book, you will see the following icons used fornetworking devices:

Throughout the book, you will see the following icons used forperipherals and other devices

Throughout the book, you will see the following icons used fornetworks and network connections.

The conventions used to present command syntax in this bookare the same conventoins used in the IOS Command Reference.The Command Reference describes these conventions as

follows:

Vertical bars (|) separate alternative, mutually exclusiveelements

indicates commands that are manually input by the user

(such as a show command).

Italics indicate arguments for which you supply actual

values

Section 1-1 aggregate-address address mask

Section 1-2 aggregate-address address mask as-set

Section 1-3 aggregate-address address mask as-set advertise-map route-map-name

map route-map-name

Figure 1-1 Aggregating Locally Sourced Routes

router bgp 1

neighbor 10.1.1.2 remote-as 2

Router B

rtrA#show ip bgp

BGP table version is 16, local router ID is 172.17.1.1

BGP table version is 6, local router ID is 172.16.3.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete

generate the prefix, we could have used only one network

command The problem with using only one network command

is that if the network goes down, the more-specific route is

withdrawn from the BGP table If the only specific route in theBGP table is withdrawn, the aggregate is withdrawn as well By

using a network command for every prefix that is contained in

the aggregate, the aggregate is advertised as long as one of themore-specific routes is up

Verification

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete

Router B withdraws this route from the BGP table but still

advertises the aggregate Assume that Router B has a defaultroute pointing to Router A and that there is no BGP route for172.16.0.0/22 to Null 0 on Router B When Router A receives an

IP packet destined for 172.16.2.x, the packet is sent to Router

B, because Router A has the aggregate 172.16.0.0/22 in its IProuting table When Router B receives the packet, it inspectsthe IP routing table to determine how to route the packet

Because 172.16.2.0/24 is down, there is no route in the routingtable Router B sends the packet to the default route, which istoward Router A When Router A receives the packet, it is sentback to B, and B sends it back to A This process continues untilthe TTL in the IP packet goes to 0 With the Null 0 route for

1 Modify the BGP configuration on Router B using redistribution

Network Next Hop Metric LocPrf Weight Path

*> 172.16.0.0/24 10.1.1.2 0 0 2 i

*> 172.16.0.0/22 10.1.1.2 0 0 2 ?

If the neighbor relationship is not in the Established state,see section 8-23.

Configuration Example: Forming an Aggregate Consisting of Prefixes from Different

Autonomous Systems

In Figure 1-4, Router A is learning about networks

172.16.0.0/24 and 172.16.1.0/24 from AS 65530 and networks172.16.2.0/24 and 172.16.3.0/24 from AS 2

Figure 1-4 Aggregate Consists of Routes

Originated in Multiple Autonomous Systems

_Router C

BGP table version is 35, local router ID is 144.223.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete

BGP table version is 13, local router ID is 172.16.3.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 172.16.0.0/24 10.1.1.1 0 1 65530 i

*> 172.16.2.0/24 0.0.0.0 0 32768 i

*> 172.16.3.0/24 0.0.0.0 0 32768 I

_rtrC#show ip bgp

BGP table version is 35, local router ID is 172.17.1.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete

rtrB#show ip bgp

BGP table version is 8, local router ID is 172.16.3.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 172.16.0.0/24 10.1.1.1 0 1 65530 i

*> 172.16.0.0/22 10.1.1.1 0 1 i

*> 172.16.2.0/24 0.0.0.0 0 32768 i

*> 172.16.3.0/24 0.0.0.0 0 32768 I

_rtrC#show ip bgp

BGP table version is 8, local router ID is 172.16.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete

state using the show ip bgp neighbors command.

If the neighbor relationship is not in the Established state,see section 8-23

In Figure 1-5, Router A is learning about networks

172.16.0.0/24 and 172.16.1.0/24 from AS 65530 and networks172.16.2.0/24 and 172.16.3.0./24 from AS 2 We will use the

advertise-map option to base the aggregate on routes

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incomplete