OSPF Network Design SolutionsSecond Edition

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Cisco Press

201 West 103rd Street Indianapolis, IN 46290 USA

Cisco Press

OSPF Network Design Solutions

Second Edition

Thomas M. Thomas II, CCIE No. 9360

0323FMf.book Page i Wednesday, March 12, 2003 9:41 AM

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ii

OSPF Network Design Solutions, Second Edition

Thomas M. Thomas II

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 First Printing April 2003

Library of Congress Cataloging-in-Publication Number: 2001095162 ISBN: 1-58705-032-3

Warning and Disclaimer

This book is designed to provide information about the Open Shortest Path First (OSPF) protocol. 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 authors, 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.

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.

Feedback Information

At Cisco Press, our goal is to create in-depth technical books of the highest quality and value. Each book is crafted with care and precision, undergoing rigorous development that involves the unique expertise of members from the professional technical community.

Readers’ feedback is a natural continuation of this process. If you have any comments regarding how we could improve the quality of this book, or otherwise alter it to better suit your needs, you can contact us through email at feedback@ciscopress.com. Please make sure to include the book title and ISBN in your message.

We greatly appreciate your assistance.

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Publisher John Wait

Editor-In-Chief John Kane

Cisco Representative Anthony Wolfenden

Cisco Press Program Manager Sonia Torres Chavez

Manager, Marketing Communications, Cisco Systems Scott Miller

Cisco Marketing Program Manager Edie Quiroz

Executive Editor Brett Bartow

Acquisitions Editor Amy Moss

Production Manager Patrick Kanouse

Development Editor Christopher Cleveland

Project Editor San Dee Phillips

Copy Editor Progressive Publishing Alternatives

Technical Editors Henry Benjamin, Matthew Birkner, Rick Burts,

Daniel Golding, John Hammond, Cary Riddock

Team Coordinator Tammi Ross

Book Designer Gina Rexrode

Cover Designer Louisa Adair

Indexer Tim Wright

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About the Author

Thomas M. Thomas II is a self-proclaimed Network Emergency Repair Dude, or NERD for short, and a country boy who is CCIE No. 9360 as well as being a certified Cisco Systems instructor and holding CCNP, CCDA, and CCNA certifications and claims he never works because he loves what he does. Tom is the founder of NetCerts.com (now CCPrep.com) and the International Network Resource Group (www.inrgi.net ) where he remains on the board of directors in an advisory capacity, providing vision and focus. He was previously an Instructor for Chesapeake Computer Consultants, Inc. (CCCI), and a course developer for Cisco Systems. He has also authored the first edition of OSPF Network Design Solutions and a variety of other networking books designed to help his fellow engineers.

Tom is currently working as a senior network consultant designing and implementing Voice-over-IP and Data networks wherever he can as a part of US Networks, Inc. (www.usnetworksinc.com). Tom currently lives in Raleigh, NC, with his family, and although he is not in the country, he humorously observes that you can see it from his home.

About the Technical Reviewers

Henry Benjamin, CCIE No. 4695, holds three CCIE certiﬁcations (Routing and Switching, ISP Dial, and Communica- tion and Services). Formerly with the Cisco Systems CCIE global team, Henry is now an independent consultant for a large security ﬁrm in Australia. He has served as a proctor for the CCIE Lab exams and is the author of CCNP Practical Studies: Routing from Cisco Press and CCIE Routing and Switching Exam Cram from Coriolis.

Matthew H. Birkner, CCIE No. 3719, is a technical leader at Cisco Systems, specializing in IP and MPLS network design. He has inﬂuenced multiple large carrier and enterprise designs worldwide. Matt has spoken at Cisco Networkers on MPLS VPN technologies in both the United States and EMEA over the past few years. Matt, a “Double CCIE,”

authored the Cisco Press book, Cisco Internetwork Design. Matt holds a B.S.E.E. from Tufts University, where he majored in electrical engineering.

Rick Burts, CCIE No. 4615, has over 20 years experience with computers and computer networks. Rick is a certiﬁed Cisco Systems instructor and a CCIE (Routing/Switching). He has taught a variety of Cisco courses and helped develop an OSPF course for Mentor Technologies. Rick is a consultant and has helped many customers with OSPF as their network routing protocol. He is a senior consultant with Chesapeake NetCraftsmen (www.netcraftsmen.net). In his current position, Rick deals with network design, implementation, and troubleshooting issues and teaches a few courses.

Daniel L. Golding is peering manager in America Online’s Internet Architecture group. Dan is responsible for ensuring worldwide Internet connectivity for all AOL Time Warner subscribers and properties. His particular areas of expertise include internetwork peering and routing policy design. He has a long history of involvement with various Internet service providers, particularly in the area of backbone engineering. Dan is also a frequent speaker at North American Network Operator’s Group (NANOG) meetings and has been a network engineer for over six years.

John Hammond has been an instructor and course developer for Juniper Networks for the past two years. Prior to that he was a member of the teaching staff of Chesapeake Computer Consultants, Inc., a Cisco Training Partner.

John has been involved in many aspects of networks since 1990.

Cary Riddock, CCNP, CSS1, has worked as an network engineer for some of the largest companies in Houston, Texas and Central Florida over the last six years. He is very active in the IT Security Field and is currently pursuing CCSP and CISSP certiﬁcations. His resume includes co-authoring MCNS for Cisco Press and is a contributing author for various network security publications.

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v

Dedications

I want to dedicate this book to my family for their ever-faithful support and understanding during the many nights and weekends I spent writing. An extra special thank you goes to my wife Rose, daughter Rebekah, and son Daniel who never voiced anything but encouragement and support.

Without the support of my family and their faith in me I would never have been able to completely rewrite this book.

I had my faith in the Lord and the knowledge that my family knew I could improve upon my book in this new edition to keep me going.

I want to reafﬁrm a few words of special meaning to my wife and I who have been married for over 15 years…

Always Forever

Endlessly

Until Eternity

Acknowledgments

I am very grateful to the group of talented people that were assembled to make this book a reality. Through their knowledge, dedication, and hard work, this book has become more than I ever thought possible.

The most important acknowledgment must go to my wife, Rose, who put up with me writing all night after working all day. Her unwavering support was the single greatest factor in my ability to complete the book you now hold in your hands.

Writing this book allowed me to assemble a team of technical professionals who have helped me make this book more than I thought possible. I had the privilege to be a part of an awesome team during this time. Thank you all for your insight and friendship.

I have to recognize the extraordinary group of publishing professionals who helped guide me through the process:

Amy Moss, a true and dear friend of many years now; and Chris Cleveland who is always busy but always has time to help me.

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Contents at a Glance

Introduction xix

Part I OSPF Fundamentals and Communication 3 Chapter 1 Networking and Routing Fundamentals 5 Chapter 2 Introduction to OSPF 47

Chapter 3 OSPF Communication 103

Part II OSPF Routing and Network Design 161 Chapter 4 Design Fundamentals 163

Chapter 5 Routing Concepts and Configuration 225 Chapter 6 Redistribution 339

Chapter 7 Summarization 405

Part III OSPF Implementation, Troubleshooting, and Management 439 Chapter 8 Managing and Securing OSPF Networks 441

Chapter 9 Troubleshooting OSPF 533

Chapter 10 BGP and MPLS in an OSPF Network 655 Part IV Additional OSPF Resources 707 Appendix A OSPF RFCs 705

Index 724

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Icons Used in This Book

Throughout this book, you will see the following icons used for networking devices:

The following icons are used for peripherals and other devices:

DSU/CSU

Router Bridge Hub DSU/CSU

Catalyst Switch

Multilayer Switch

ATM Switch

ISDN/Frame Relay Switch

Communication Server

Gateway Access

Server

PC PC with

Software

Sun Workstation

Macintosh

Terminal File

Server

Web Server

Cisco Works Workstation

Printer Laptop IBM

Mainframe

Front End Processor

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The following icons are used for networks and network connections:

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.

• Boldfaceindicates commands and keywords that are entered literally as shown. In actual conﬁguration examples and output (not general command syntax), boldface indicates commands that are manually input by the user (such as a show command).

• Italics indicate arguments for which you supply actual values.

Network Cloud Token

Ring Token Ring Line: Ethernet

FDDI

FDDI Line: Serial

Line: Switched Serial

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xix

Introduction

OSPF is in use in numerous networks worldwide. OSPF is also one of the most widely tested on protocols if you choose to pursue a networking certification. From a technical perspective, the overwhelming presence of OSPF ensures that almost everyone will encounter it at some point in their career. A result of these facts is that everyone should understand OSPF including how it operates, how to configure it, troubleshooting, and—most importantly—how to design a network that will use OSPF. You can see that everyone will be exposed to OSPF to some degree, and because it is highly likely that your family is surfing the Internet and having their packets pass over a network that is OSPF enabled, it is clear to me that they, too, might benefit from this book, so consider getting them a copy as well.

Who Should Read This Book?

This book is not designed to be a general networking topics book; although, it can be used for that purpose.

This book is intended to tremendously increase your knowledge level with regards to OSPF. Personnel responsible for understanding OSPF should read this book. You might need to understand OSPF because you are a programmer, network manager, network engineer, studying for certiﬁcation, and so on.

How This Book Is Organized

Although this book can be read cover-to-cover, it is designed to be ﬂexible and allow you to easily move between chapters and sections of chapters to cover just the material that you need more information on.

If you do intend to read them all, the order in the book is an excellent sequence to use:

• Chapter 1, “Networking and Routing Fundamentals”—Those of us responsible for

programming, managing, maintaining, troubleshooting, and ensuring the operation of the network will appreciate this chapter as the building blocks of interworking are reviewed.

• Chapter 2, “Introduction to OSPF”—This chapter helps you understand the basic types of routing protocols, their characteristics, and when it is best to use a certain protocol and uses that information to build a deeper understanding of how to implement them in your network.

• Chapter 3, “OSPF Communication”—This chapter introduces you to how OSPF communicates between routers running OSPF. This chapter covers how the link-state information is then entered into the link-state database through OSPF’s use of Link-State Advertisement (LSA) and the various internal OSPF protocols that deﬁne and allow OSPF routers to communicate.

• Chapter 4, “Design Fundamentals”—The foundation of understanding the purpose for using OSPF and its operation as discussed in previous chapters is further expanded as the discussion of OSPF performance and design issues are expanded. Within each of the design sections, a series of

“golden design rules” are presented. These rules can help you understand the constraints and recommendations of properly designing each area within an OSPF network. In many cases, examples are presented that draw upon the material presented, to further reinforce key topics and ideas.

• Chapter 5, “Routing Concepts and Conﬁguration”—This is going to be a fun chapter that will challenge you, the reader, and me, the author, to keep you interested in the different. We are going to look at all the OSPF features, knobs, and functionality that are possible.

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• Chapter 6, “Redistribution” and Chapter 7, “Summarization”—Redistribution and

summarization are interesting concepts, and these chapters decipher and demystify the challenges you face when one routing algorithm is redistributed into another, when one of those protocols is OSPF (of course), or when the OSPF routing table is optimized through summarization.

• Chapter 8, “Managing and Securing OSPF Networks”—The management of your OSPF network is just as important as the security. In fact, a case could be made that proper network management is the most important aspect of having your network operate smoothly.

• Chapter 9, “Troubleshooting OSPF”—This chapter builds upon the design theories and OSPF communication processes as discussed throughout the book prior to this chapter. The basis for this chapter is how to go about monitoring OSPF to ensure it is operating correctly and what to do if it is not. There are certain troubleshooting procedures and techniques that you can use to determine the causes of a network problem, which are covered as well.

• Chapter 10, “BGP and MPLS in an OSPF Network”—This chapter covers some of the evolving OSPF extensions and new capabilities as OSPF grows to embrace new technologies such as Multiprotocol Label Switching (MPLS). This chapter begins this discussion by reviewing the difference between an IGP and an EGP routing protocol, and then looks at how OSPF interacts with BGP.

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I

P A R T

OSPF Fundamentals and Communication

Chapter 1 Networking and Routing Fundamentals

Chapter 2 Introduction to OSPF

Chapter 3 OSPF Communication

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C H A P T E R 1

Networking and Routing Fundamentals

Achievement: Unless you try to do something beyond what you have already mastered, you will never grow.—Successories

In recent years, the growth of networks everywhere has accelerated as many organizations move into the international business arena and join the Internet community. This expansion continues to drive the development, reﬁnement, and complexity of network equipment and software, consequently resulting in some unique issues and exciting advances. You rarely see an advertisement that does not contain the famous www preﬁx. In my hometown, one of the local news stations now displays the e-mail address of its reporters as they deliver the news! Is this the new economy in action, or is it just another example of too much information? At least the media are feeding on their own now!

Can you imagine modern business or life without computers, fax machines and services, e-mail, Internet commerce, automatic teller machines, remote banking, check cards, or video conferencing? Even more importantly, today’s children think that these tools are commonplace and that business cannot be done without them when they get to our age. I hate to admit it, but I can clearly remember a time without the Internet and when Novell ruled the ofﬁce; however, nothing stands still in our industry, and some of us have known that for quite a while.

Gordon Moore of Intel made an interesting observation in 1965, just 6 years after he invented the ﬁrst planar transistor. He observed that the “doubling of transistor density on a manufactured die every year” would occur. Now almost 40 years later, his statement has become known as Moore’s law, and it has continued to hold true. According to Intel

There are no theoretical or practical challenges that will prevent Moore’s law from being true for another 20 years; this is another ﬁve generations of processors.

In 1995, Moore updated his prediction to indicate that transistor density would double once every two years. Using Moore’s law to predict transistor density in 2012, Intel should have the capability to integrate 1 billion transistors on a production die that will be operating at 10 GHz. This could result in a performance of 100,000 MIPS. This represents an increase over the Pentium II processor that is similar to the Pentium II processor’s speed increase over the 386 chip. That is impressive considering the sheer number of transistors on a chip that you can hold in your hand! Figure 1-1 depicts Moore’s law.

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Figure 1-1 Moore’s Law

Foundations of Networking

Many advanced features are being supported by the physical hardware through the appli- cation of Moore’s law. Those of us responsible for networking these many devices follow a theoretical framework that allows the required functionality to be deployed within our networks. This framework is more commonly known as the OSI reference model.

OSI stands for open system interconnection, where open system refers to the speciﬁcations surrounding the model’s structure as well as its nonproprietary public availability. Anyone can build the software and hardware needed to communicate within the OSI structure. If you know someone that has written a script to access information in a router, at some level, he is following the OSI reference model.

Why Was the OSI Reference Model Needed?

Before the development of the OSI reference model, the rapid growth of applications and hardware resulted in a multitude of vendor-speciﬁc models. In other words, one person’s solution would not work with anyone else’s because there was no agreed-upon method, style, process, or way for different devices to interoperate. In terms of future network growth and design, this rapid growth caused a great deal of concern among network engineers and designers because they had to ensure that the systems under their control could interact with every standard. This concern encouraged the International Organization of Standardization (ISO) to initiate the development of the OSI reference model.

100,000

10,000

1000

100

10

1

4004 8086

80,286 80,386

80,486

Intel CPUs ^{2.5 years}

Thousands of Transistors

Year: 1975 1980 1985 1990 1995 2000 Doubling time of fitted line is 2.0 years.

P5 (Pentium)

P6 (Pentium Pro)

P7 (Merced)

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Foundations of Networking 7

The work on the OSI reference model was initiated in the late 1970s and came to maturity in the late 1980s and early 1990s. The ISO was the primary architect of the model that is in place today.

Characteristics of the OSI Layers

Figure 1-2 demonstrates how the layers are spanned by a routing protocol. You might also want to contact Network Associates, as its protocol chart shows how almost every protocol spans the seven layers of the OSI reference model. Figure 1-2 provides a good illustration of how the seven layers are grouped in the model. For a better picture of how protocols are positioned in the OSI reference model, visit to the following websites and request a copy of the applicable posters:

Acterna (aka W&G) offers free OSI, ATM, ISDN, and ﬁberoptics posters at www.acterna.com/shared/forms/poster_form.html.

Network Associates offers its Guide to Communications Protocols at www.sniffer.com/dm/protocolposter.asp.