Table Of Content,TITLE.23706 Page i Wednesday, January 9, 2002 12:29 PM
IP Routing
,COPYRIGHT.23443 Page iv Wednesday, January 9, 2002 12:29 PM
IP Routing
by Ravi Malhotra
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,TITLE.23706 Page iii Wednesday, January 9, 2002 12:29 PM
IP Routing
Ravi Malhotra
Beijing • Cambridge • Farnham • Köln • Paris • Sebastopol • Taipei • Tokyo
,AUTHOR.COLO.23272 Page 1 Wednesday, January 9, 2002 12:28 PM
About the Author
Ravi Malhotra ([email protected]) began working for AT&T Bell Labs in 1986,
doing R&D work. Since then he has taught data communications at universities,
managed IP networks for several large financial houses, and written several maga-
zine assignments. Mr. Malhotra possesses degrees in Electrical Engineering and
Computer Science.
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,p_ip_routingTOC.fm.23063 Page vii Wednesday, January 9, 2002 12:27 PM
Table of Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
1. Starting Simple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
What Is IP Routing? 1
Directly Connected Networks 2
Static Routing 3
Dynamic Routing 5
The Routing Table 6
Underlying Processes 9
Summing Up 9
2. Routing Information Protocol (RIP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Getting RIP Running 10
How RIP Finds Shortest Paths 13
Convergence 19
Subnet Masks 26
Route Summarization 27
Default Route 28
Fine-Tuning RIP 29
Summing Up 31
3. Interior Gateway Routing Protocol (IGRP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Getting IGRP Running 33
How IGRP Works 37
Speeding Up Convergence 55
Route Summarization 56
Default Routes 57
vii
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Classful Route Lookups 60
Summing Up 61
4. Enhanced Interior Gateway Routing Protocol (EIGRP) . . . . . . . . . . . . . . . . . . 63
Getting EIGRP Running 64
EIGRP Metric 67
How EIGRP Works 68
Variable Length Subnet Masks 82
Route Summarization 84
Default Routes 88
Troubleshooting EIGRP 90
Summing Up 93
5. Routing Information Protocol Version 2 (RIP-2). . . . . . . . . . . . . . . . . . . . . . . . 94
Getting RIP-2 Running 95
RIP-2 Packet Format 98
RIP-1/RIP-2 Compatibility 99
Classful Versus Classless Routing Protocols 101
Classful Versus Classless Route Lookup 103
Authentication 103
Route Summarization 105
Summing Up 106
6. Open Shortest Path First (OSPF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Getting OSPF Running 109
OSPF Metric 113
Definitions and Concepts 114
How OSPF Works 121
Route Summarization 137
Default Routes 140
Virtual Links 141
Demand Circuits 143
Stub, Totally Stubby, and Not So Stubby Areas 144
NBMA Networks 148
OSPF Design Heuristics 150
Troubleshooting OSPF 153
Summing Up 156
viii | Table of Contents
,p_ip_routingTOC.fm.23063 Page ix Wednesday, January 9, 2002 12:27 PM
7. Border Gateway Protocol 4 (BGP-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Background 158
Getting BGP Running 163
How BGP Works 166
Load Balancing 191
Route-Filtering 192
Connecting to the Internet 194
Choosing an ISP 199
Troubleshooting BGP 200
Summing Up 202
8. Administrative Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
Filter Routing Information 204
Rate the Trustworthiness of a Routing Information Source 207
Redistribute Routes 207
Maximum Number of Paths 211
Summing Up 211
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Table of Contents | ix
,DEDICATION.23573 Page v Wednesday, January 9, 2002 12:29 PM
Thisbookisdedicatedtomygrandfather,thelate
P.D.Gandhi,whotaughtmetheloveoflearning.
,ch00.21432 Page xi Wednesday, January 9, 2002 12:23 PM
Preface
Ants, single-celled creatures such as the cellular slime mold, plants and animals in
ecosystems,and(even)humanbeingscancongregateanddisplaymiraculouslycom-
plexbehaviors.*Sayacolonyofantsinatreeneedstomovetoanothertree,perhaps
insearchoffood.Someantsbuildabridgebyjoiningtheirbodiesinachainstretch-
ing from one limb in one tree to another limb in another tree. Other ants cross over
this ant structure, walking over their peers. Once all the ants have crossed over, the
ants in the bridge begin to gracefully undo the structure, crossing one by one. Each
ant only repeats simple actions, over and over again; the net result of thousands of
ants working together is the miracle of the bridge, which allows the ant colony to
migrate.
Inourownhumansocietywehopetoemulatethislevelofcooperation.Eachoneof
usisusefultoothersinsomeway:wewrite,laybricks,actinthetheater,farm,drive
buses,repairhelicopters,tendtothesick,makecoffee...Asindividuals,werepeatthe
sameactsagainandagain,whetheritbemakingcoffeecupaftercoffeecuporseeing
patient after patient. The net result of all these acts is our complex, wonderful society.
So, what does all this have to do with IP routing? Each router in a network repeats
simpleprocessesoverandoveragain,asdescribedinthespecificationoftherouting
protocolitisexecuting.Thenetresultofalltheroutersinanetworkrepeatingthese
simple processes is IP routing, or the movement of IP packets in a network.
* TheNewYorkTimeshasreportedsomeintriguingexamplesofsuchbehavior,quotingresearchworkfromthe
SantaFeInstituteinNewMexico(“MindlessCreaturesActingMindfully,”TheNewYorkTimes,March23,
1999, Science Times).
xi
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