Tài liệu Internet Routing Architectures pptx

IV: Internet Routing Device Configuration

265
11. Configuring Basic BGP Functions and Attributes
Building Peering Sessions
Route Filtering and Attribute Manipulation
Peer Groups
Sources of Routing Updates
Overlapping Protocols: Backdoors
BGP Attributes
BGP-4 Aggregation
Looking Ahead

266
267
271
280
282
289
290
302
319
12. Configuring Effective Internet Routing Policies
Redundancy, Symmetry, and Load Balancing
Following Defaults Inside an AS
Policy Routing
Route Reflectors
Confederations
Controlling Route and Cache Invalidation
BGP Outbound Request Filter Capability
Route Dampening
Looking Ahead

320
321
347
361
364
367
372
378
379
383
V: Appendixes

384
A. BGP Command Reference

385
B. References for Further Study
Interesting Organizations
Research and Education
Miscellaneous
Books
Internet Request For Comments

390
390
390
390
391
391
C. BGP Outbound Route Filter (ORF)
When to Use BGP ORF
Configuration
EXEC Commands
Closing Remarks

394
394
394
396
397
D. Multiprotocol BGP (MBGP)
The Motivation Behind the New Command-Line Interface
Organizing Command Groups in the New Configuration
Peer Groups
Route Maps
Redistribution
Route Reflector
Aggregation
List of BGP Commands
Upgrading to the AF Style

398
398
399
403
404
405
407
407
408
409
Internet Routing Architectures, Second Edition
page 1
About the Technical Reviewers
Alexei Roudnev is currently a Software System Engineer for Genesys Labs/Alcatel group in,
San Francisco, California. He worked for 10 years as a Network Engineer at Relcom
Network, one of the creators of the Russian Internet, in Moscow, Russia. Alexei was also a
UNIX based systems Software Developer in Moscow for 9 years.
Abha Ahuja is currently a Senior Network Engineer at Internap Network Services. She
works on network design, architecture and operational issues. Previous to Internap, she
worked at Merit Network, a leading network research institution where she worked on the
Route Server Next Generation project, a nationwide deployment of routing servers at
exchange points, and the Internet Performance Measurement and Analysis (IPMA) project.
She continues to play an active role in the Internet community and pursues research interests
including inter-domain routing behavior and protocols, network operations and performance
statistics, and network security. She is a skilled network engineer, certified troublemaker and
a classic Scorpio.

Internet Routing Architectures, Second Edition
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Acknowledgments
This book would not have been possible without the help of many people whose comments
and suggestions significantly improved the end result. First, we would like to thank Abha
Ahuja, Shane Amante, Johnson Liu, Alvaro Retana, and Alexander Rudenev for their
exceptional technical review of this manuscript. We would also like to explicitly acknowledge
Henk Smit, Bruce Cole, Enke Chen, Srihari Ramachandra, Rex Fernando, Satinder Singh, and
Ravi Chandra, as well as the entire Cisco "BGP Coders" group, and everyone else who
provided any amount of input for the second edition. Also, we would like to acknowledge the
overwhelming support and patience of Danny McPherson's present employer, Amber
Networks, and previous employer, Qwest Communications, both of which had a significant
impact on the value of the content. Finally, we would like to thank Christopher Cleveland,
Tracy Hughes, Marc Fowler, Gayle Johnson, and the rest of the Cisco Press folks for keeping
us on track and getting the book published.

Internet Routing Architectures, Second Edition
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Introduction
The Internet, an upstart academic experiment in the late 1960s, struggles with identity and
success today. From the ARPANET to the NSFnet to ANYBODYSNET, the Internet is no
longer owned by a single entity; it is owned by anybody who can afford to buy space on it.
Tens of millions of users are seeking connectivity, and tens of thousands of companies are
feeling left out if they do not tap into the Internet. This has put network designers and
administrators under a lot of pressure to keep up with networking and connectivity needs.
Understanding networking, and especially routing, has become a necessity.
Some people are surprised when networks fail and melt down, but others are surprised when
they don't. This seems to be the case because there is so little useful information out there.
Much of the information on routing that has been available to designers and administrators up
until now is doubly frustrating: The information makes you think you know how to build your
network—until you try, and find out that you don't. The first edition of this book addressed
real routing issues, using real scenarios, in a comprehensive and accessible way.
In addition to providing a thorough update to the original material, this edition introduces
recent enhancements to the BGP protocol, discusses changes surrounding registration and
allocation of Internet numbers, and provides additional information on research and
educational networks.
Objectives
The purpose of this book is to make you an expert on integrating your network into the global
Internet. By presenting practical addressing, routing, and connectivity issues both
conceptually and in the context of practical scenarios, this book aims to foster your
understanding of routing so that you can plan and implement major network designs in an
objective and informed way. Whether you are a customer or a provider (or both) of Internet
connectivity, this book anticipates and addresses the routing challenges facing your network.
Audience
This book is intended for any organization that might need to tap into the Internet. Whether
you are becoming a service provider or are connecting to one, you will find all you need to
integrate your network. The perspectives of network administrators, integrators, and architects
are considered throughout this book. Even though this book addresses different levels of
expertise, it progresses logically from the simplest to the most challenging concepts and
problems, and its common denominator is straightforward, practical scenarios to which
anyone can relate. No major background in routing or TCP/IP is required. Any basic or
background knowledge needed to understand routing is developed as needed in text
discussions, rather than assumed as part of the reader's repertoire.
Organization
The book is organized into four parts:

Internet Routing Architectures, Second Edition
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•
Part I: The Contemporary Internet—
Chapters 1 through 3 cover essential introductory aspects of the contemporary Internet
with respect to its structure, service providers, and addressing. Even if you are already
familiar with the general structure of the Internet, you are encouraged to read the
portions of Chapter 1 concerning Network Access Points, the Routing Arbiter Project,
and Network Information Services. The pressures that precipitated these components
of the Internet have continuing practical implications for routing design problems
faced by administrators. Chapter 2 provides valuable criteria by which to evaluate
Internet service providers. If you represent such a provider, or are already a customer
of one, some of the information might be familiar to you already. Chapter 3 discusses
classless interdomain routing (CIDR), VLSM (variable-length subnet masks), IPv6,
and other aspects of Internet addressing.
• Part II: Routing Protocol Basics—
Chapters 4 and 5 cover the basics: properties of link-state and distance vector routing
protocols and why interdomain routing protocols are needed and how they work.
These topics are covered both generally and in the specific context of BGP (Border
Gateway Protocol)—the de facto standard interdomain routing protocol used in the
Internet today. BGP's particular capabilities and attributes are thoroughly introduced.
• Part III: Effective Internet Routing Designs—
Chapters 6 through 10 delve into the practical, design-oriented applications of BGP.
The BGP attributes introduced in Part II are shown in action, in a variety of
representative network scenarios. BGP's attributes are put to work in implementing
design goals such as redundancy, symmetry, and load balancing. The challenges of
making intradomain and interdomain routing work in harmony, managing growing or
already-large systems, and maintaining stability are addressed.
• Part IV: Internet Routing Device Configuration—
Chapters 11 and 12 contain numerous code examples of BGP's attributes and of
various routing policies. The code examples will make the most sense to you after you
have read the earlier chapters, because many of them address multiple concepts and
design goals. So that you can juxtapose textual discussions from earlier chapters with
the code examples in Chapters 11 and 12, pointers called "Configuration Examples"
appear in the earlier chapters. When you see one, you might want to fast-forward to
the referenced page to see a configuration example of the attribute or policy being
discussed.
Finally, several appendixes provide additional references for further reading, an up-to-date
Cisco IOS™ BGP command reference, and information regarding IOS™ modifications
intended to provide a more intuitive BGP command-line interface.
Approach
It is very hard to write about technical information in an accessible manner. Information that
is stripped of too much technical detail loses its meaning, but complete and precise technical
Internet Routing Architectures, Second Edition
page 5
detail can overwhelm readers and obscure concepts. This book introduces technical detail
gradually and in the context of practical scenarios whenever possible. The most heavily
technical information—configuration examples in the Cisco IOS language—is withheld until
the final two chapters of this book so that it is thoroughly grounded in the concepts and
sample topologies that precede it.
Although your ultimate goal is to design and implement routing strategies, it is critical to
grasp concepts and principles before applying them to your particular network. This book
balances conceptual and practical perspectives by following a logical, gradual progression
from general to specific, and from concepts to implementation. Even in chapters and sections
that necessarily take a largely descriptive approach, hands-on interests are addressed through
pointers to configuration examples, frequently asked questions, and scenario-based
explanations.
The scenario-based approach is an especially important component of this book: it utilizes
representative network topologies as a basis for illustrating almost every protocol attribute
and routing policy discussed. Even though you might not see your exact network situation
illustrated, the scenario is specific enough to facilitate learning by example, and general
enough that you can extrapolate how the concepts illustrated apply to your situation.
Features and Text Conventions
This book works hard not to withhold protocol details and design-oriented information, while
at the same time recognizing that building general and conceptual understanding necessarily
comes first. Two features are included to help emphasize what is practical and design-oriented
as underlying concepts are developed:
• Pointers to configuration examples—Located close to pertinent text discussions, these
references point forward to places in Chapters 11 and 12 where related configuration
examples can be found.
• Frequently Asked Questions—Located at the end of every chapter, these questions
anticipate practical and design-oriented questions you might have, for your particular
network, after having read the chapter.
Command Syntax Conventions
The conventions used to present command syntax in this book are the same conventions used
in the IOS 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 n optional elements.
• Boldface indicates 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 indicates arguments for which you supply actual values.

Internet Routing Architectures, Second Edition
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Icons Used in This Book

Throughout the book, you will see the following icons used for peripherals and other devices.


Internet Routing Architectures, Second Edition
page 7
Throughout the book, you will see the following icons used for networks and network
connections.


Internet Routing Architectures, Second Edition
page 8
Part I: The Contemporary Internet
The complexity of routing problems and solutions is tied closely to the growth and evolution
of the contemporary Internet. Thus, before delving into specifics about routing protocols, you
will find it extremely useful to have some general perspective and background information.
Such historical developments as the Route Arbiter project, Network Access Points, and
Network Information Services, covered in Chapter 1, continue to have extremely practical
implications for organizations that want to be connected to global networks. Chapter 2
introduces general and network topology issues associated with Internet service providers.
Chapter 3 covers concepts of addressing and classless interdomain routing, which are needed
to control the depletion of the IP address space

Internet Routing Architectures, Second Edition
page 9
Chapter 1. Evolution of the Internet
This chapter covers the following key topics:
• Origins and recent history of the Internet—
A brief history of the early Internet, with emphasis on its implementers and users, as
well as how it has evolved in the last decade. Includes an overview of several
important NSF solicitations.
• Network Access Points—
Internet service providers can connect, directly or indirectly, with Network Access
Points (NAPs). You will need to know enough to evaluate how your ISP connects to
the NAPs, as well as which NAPs are available in which regions of the world today.
• Direct interconnections—
An alternative to NAPs, this connection model has gained popularity with large
service providers in recent years, primarily because it overcomes some of the
shortcomings of the public NAP connection model.
• Routing arbiter project—
An overview of concepts central to the rest of this book: route servers and the Routing
Arbiter Database. Route servers are architectural components of NAPs, Internet
service providers, and other networks.
• Regional providers—
Background on the current Internet layout with respect to regional connections.
• Information services—
An overview of the information services and agencies that have evolved as a result of
NSF solicitation and privatization of the Internet: the InterNIC, registration services,
directory and database services, NIC support services, and the evolution of other
Internet registries and the Internetworking Routing Registries.
• The once and future Internet—
A survey of research efforts that point to the future of the Internet: The Next-
Generation Initiative, Internet2, and Abilene.
The structure and makeup of the Internet has adapted as the needs of its community have
changed. Today's Internet serves the largest and most diverse community of network users in
the computing world. A brief chronology and summary of significant components are

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