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An Essential Guide to Understanding and Implementing IP Routing Protocols
Cisco’s authoritative single-source guide to IP routing protocols for enterprise and service provider environments
Service providers and large enterprises are converging on a common IP infrastructure that supports rapid deployment of high-value services. Demand is soaring for highly skilled IP network engineers who can implement and run these infrastructures. Now, one source combines reliable knowledge about contemporary IP routing protocols and expert hands-on guidance for using them with Cisco IOS, IOS XE, and IOS XR operating systems.
After concisely reviewing the basics, three Cisco experts fully explain static routing, EIGRP, OSPF, IS-IS, and BGP routing protocols. Next, they introduce advanced routing with policies and redistribution, sophisticated BGP-based traffic engineering, and multicast. They present comprehensive coverage of IPv6, from its multicast implementation to its completely revamped address structure. Finally, they discuss advanced high availability techniques, including fast routing convergence.
IP Routing on Cisco IOS, IOS XE, and IOS XR presents each protocol conceptually, with intuitive illustrations, realistic configurations, and appropriate output. To help IOS users master IOS XE and IOS XR, differences in operating systems are explicitly
identified, and side-by-side feature command references are presented.
All content fully aligns with Learning@Cisco, providing efficient self-study for multiple Cisco Career Certifications, including CCNA®/CCNP®/CCIE® Service Provider, CCIE Routing & Switching, Cisco IOS XR Specialist Certification, and the routing components of several additional Cisco Certifications.
Brad Edgeworth, CCIE No. 31574 (R&S & SP) has been with Cisco since 2011 as Systems Engineer and Technical Leader. Formerly a network architect and consultant for various Fortune® 500 companies, his 18 years of IT experience includes extensive architectural and operational work in enterprise and service provider environments. He is a Cisco Live distinguished speaker presenting on IOS XR.
Aaron Foss, CCIE No. 18761 (R&S & SP), a High Touch Engineer with the Cisco Focused Technical Support (FTS) organization, works with large service providers to troubleshoot MPLS, QoS, and IP routing issues. He has more than 15 years of experience designing, deploying, and troubleshooting IP networks.
Ramiro Garza Rios, CCIE No. 15469 (R&S, SP, and Security), Senior Network Consulting Engineer with Cisco Advanced Services, plans, designs, implements, and optimizes next-generation service provider networks. Before joining Cisco in 2005, he was Network Consulting and Presales Engineer for a Cisco Gold Partner in Mexico, where he planned and deployed both enterprise and service provider networks.
Foreword by Norm Dunn, Senior Product Manager, Learning@Cisco Global Product Management, Service Provider Portfolio
Contents
Foreword
Introduction
Part I Network Fundamentals
Chapter 1 Introduction to the Operating Systems 1
IOS, IOS XE, and IOS XR Software Architecture 1
IOS 1
Kernel and OS Scheduling 2
Memory Management 2
Software Packaging 2
IOS XE 4
Kernel and OS Scheduling 4
Memory Management 4
IOS XR 5
Kernel and OS Scheduling 5
Memory Management 5
Software Packaging 6
Debugging 8
CLI and Configuration 8
IOS 9
User Mode 9
Privileged Mode 10
Global Configuration Mode 10
Configuration Archiving 11
Configuration Replace 13
IOS XR 14
Viewing Changes in the SysDB 17
Commit Label 18
Commit Replace 19
Failed Commits 20
Configuration Rollback 21
Commit Confirmed 22
Multiple Commit Options 23
Loading Files for Changes 24
Hierarchical Configuration 24
PWD 26
Root 26
Summary 27
References in This Chapter 27
Chapter 2 IPv4 Addressing 29
IP Fundamentals 29
Understanding Binary 31
Address Classes 34
Subnet Masks and Subnetting 35
Subnet Mask Purpose 36
Calculating Usable IP Addresses 37
Network Prefix Notation 38
Subnetting 38
Subnet Field 39
Subnet Math 41
Subnet Design 46
Classless Interdomain Routing 49
Classful Versus Classless Routing 50
Classful Routing 50
Classless Routing 53
Variable-Length Subnet Masks 55
Summarization 56
Private IP Addressing 58
Special IP Addresses 59
IPv4 Address Configuration 60
Wildcard Subnet Masks 62
Summary 64
References in This Chapter 65
Chapter 3 How a Router Works 67
IP Routing 67
Distance Vector Algorithms 69
Enhanced Distance Vector Algorithm 70
Link-State Algorithms 70
Path Vector Algorithm 71
Routing Table 72
Prefix Length 73
Administrative Distance 73
Metrics 75
Virtual Routing and Forwarding 76
IP Packet Switching 83
Process Switching 84
Cisco Express Forwarding 85
Software CEF 87
Hardware CEF 88
Planes of Operation 89
References in This Chapter 90
Part II Routing Protocols
Chapter 4 Static Routing 91
Connected Networks 91
Secondary Connected Networks 94
Static Routing Fundamentals 94
Point-to-Point Interfaces 96
Broadcast Interfaces 98
Default Route 99
Floating Static Routing 103
Recursive Lookup 105
Multihop Routing 108
Single Recursive Lookup 108
Multiple Recursive Lookups 109
Problems with Static Route Recursion 112
Null Interface 116
Static VRF Routes 121
References in This Chapter 124
Chapter 5 EIGRP 125
EIGRP Fundamentals 125
EIGRP Neighbors 126
Inter-Router Communication 126
Forming EIGRP Neighbors 128
Classic EIGRP Autonomous System Configuration 131
IOS network Statement 132
IOS XR 134
Passive Interfaces 134
Sample Topology and Configuration 134
Confirmation of Interfaces 136
Verification of EIGRP Neighbor Adjacencies 139
Display of Installed EIGRP Routes 140
Router ID 141
EIGRP Terminology 142
Topology Table 143
Path Metric Calculation 145
Custom K Values 148
Interface Delay Settings 149
Load Balancing 151
EIGRP Wide Metrics 153
Failure Detection and Timers 155
Convergence 156
Stuck in Active 159
Stub 160
Design Considerations with EIGRP Stubs 164
Summarization 166
Interface-Specific Summarization 166
Summarization Metrics 171
Advertising a Default Route 172
Automatic Summarization 172
Authentication 174
Enabling Authentication on the interface 174
Key Chain Configuration 174
WAN Considerations 177
IP Bandwidth Percent 177
Split Horizon 179
Next-Hop Self 182
EIGRP Named Configuration 184
Address Family Instance Configuration 185
Address Family Interface Configuration 186
Address Family Topology Configuration 188
Summary 189
References in This Chapter 189
Chapter 6 OSPF 191
OSPF Fundamentals 191
Inter-Router Communication 193
OSPF Hello Packets 194
Router ID 195
Neighbors 196
Forming OSPF Neighbor Adjacencies 197
Basic OSPF Configuration 202
IOS network Statement 202
IOS Interface Specific 204
IOS XR 205
Passive Interfaces 205
Sample Topology and Configuration 206
Confirmation of Interfaces 208
Verification of OSPF Neighbor Adjacencies 209
Verification of OSPF Routes 211
Designated Router and Backup Designated Router 212
Designated Router Elections 214
DR and BDR Placement 216
Failure Detection 219
Hello Timer 219
Dead Interval Timer 219
Verifying OSPF Timers 220
OSPF Fast Packet Hellos 220
OSPF Network Types 221
Broadcast 221
Non-Broadcast 222
Point-to-Point Networks 224
Point-to-Multipoint Networks 225
Loopback Networks 229
Review of OSPF Network Types 231
OSPF Adjacency with Different OSPF Network Types 231
Link Costs 235
Authentication 236
IOS Support for OSPF Authentication 236
IOS XR Support for OSPF Authentication 236
Summary 239
References in This Chapter 240
Chapter 7 Advanced OSPF 241
Areas 241
Area ID 245
OSPF Route Types 246
External OSPF Routes 247
Link-State Announcements 249
LSA Age and Flooding 251
LSA Types 251
LSA Type 1: Router Link 252
LSA Type 2: Network Link 257
LSA Type 3: Summary Link 259
LSA Type 5: External Routes 263
LSA Type 4: ASBR Summary 265
LSA Type 7: NSSA External Summary 268
LSA Type Summary 270
OSPF Path Selection 270
Intra-Area Routes 271
Interarea Routes 272
External Route Selection 272
E1 and N1 External Routes 273
E2 and N2 External Routes 273
Equal Cost Multi-Path 274
Summarization of Routes 274
Interarea Summarization 276
External Summarization 280
Default Route 283
OSPF Stubby Areas 286
Stub Areas 286
Totally Stubby Areas 289
Not-So-Stubby Areas 292
Totally NSSA Areas 295
Virtual Links 298
Discontiguous Network 301
Multi-Area Adjacency 304
Prefix Suppression 308
Summary 313
References in This Chapter 314
Chapter 8 IS-IS 315
IS-IS Fundamentals 315
Areas 318
OSI Addressing 319
Inter-Domain Part 320
Domain Specific Part 321
NET Addressing 322
Inter-Router Communication 323
IS Protocol Header 325
TLVs 326
IS PDU Addressing 326
Hello Packets 327
Link-State Packets 329
LSP Lifetime 329
LSP ID 330
LSP Sequence 331
Attribute Fields 331
LSP Packet and TLVs 332
IS-IS Neighbor 333
Ethernet 333
Point-to-Point 338
Basic IS-IS Configuration 340
IOS 340
IOS XR 340
Sample Topology and Configuration 341
Confirmation of IS-IS Interfaces 343
Verification of IS-IS Neighbor Adjacencies 346
Verification of IS-IS Routes 347
Designated Intermediate System 348
DIS Elections 351
DIS Placement 352
Point-to-Point Adjacency on Broadcast Media 353
Link State Packet Database 355
Viewing the LSPDB 356
Non-Pseudonode LSPs 357
Pseudonode LSPs 358
Building the Topology 359
Viewing the Topology 360
SPF Calculations 361
Passive Interfaces 362
Removal of Hello Padding 364
Failure Detection 366
Hello Timer 366
Hello Multiplier and Holding Timer 367
Authentication 367
IS-IS Hello Authentication 367
IS-IS LSP Authentication 368
Summary 371
References in This Chapter 372
Chapter 9 Advanced IS-IS 373
Advanced IS-IS Routing 373
Route Leaking 377
Backbone Continuity 380
Loop Prevention 382
Router-Specific IS-IS Levels 384
Interface Specific IS-IS Levels 385
Path Selection 386
Equal Cost Multi-Path 387
Interface Metrics 387
Overload Bit 394
Summarization 396
Default Routes 400
Prefix Suppression 401
Summary 405
References in This Chapter 406
Chapter 10 Border Gateway Protocol (BGP) 407
BGP Fundamentals 408
Autonomous System Numbers 408
Path Attributes 409
Loop Prevention 409
Address Families 410
Inter-Router Communication 410
Open Messages 412
Hold Time 412
BGP Identifier 413
Keepalive Messages 413
Update Messages 413
Notification Messages 414
BGP Sessions 415
BGP Neighbor States 415
Idle State 415
Connect State 415
Active State 416
OpenSent State 416
OpenConfirm State 417
Established State 417
Basic BGP Configuration 418
IOS 419
IOS XR 420
Verification of BGP Sessions 421
Prefix Advertisement 425
Receiving and Viewing Routes 427
iBGP 431
iBGP Full-Mesh Requirement 432
Peering via Loopback Addresses 433
eBGP 438
eBGP and iBGP Topologies 442
Next-Hop Manipulation 444
iBGP Scalability 446
Route Reflectors 446
Loop Prevention in Route Reflectors 451
Out-of-Band Route Reflectors 453
Confederations 453
Failure Detection 459
Security 459
eBGP Multihop 459
TTL Security 461
Summary 463
References in This Chapter 465
Part III Advanced Routing Techniques
Chapter 11 Route Maps and Route Policy 467
Access Control Lists 467
Standard ACLs 468
Extended ACLs 469
IGP Network Selection 469
BGP Network Selection 470
Prefix Matching 471
Prefix Lists 473
Prefix Sets 474
Regular Expressions 475
_ (Underscore) 477
^ (Caret) 478
$ (Dollar Sign) 478
[ ] (Brackets) 479
- (Hyphen) 479
[^] (Caret in Brackets) 480
( ) (Parentheses and | Pipe) 480
. (Period) 481
+ (Plus Sign) 481
? (Question Mark) 481
* (Asterisk) 482
Looking Glass and Route Servers 483
AS_Path Access List 484
IOS XR AS_Path Selection Options 484
is-local 485
length 485
unique-length 486
passes-through 486
neighbor-is 487
originates-from 487
AS Path Set 488
Route Maps 488
Conditional Matching 490
Multiple Conditional Match Conditions 491
Complex Matching 491
Optional Actions 492
Continue 493
Route Map Examples 494
Routing Policy Language 496
Route Policy Structure 496
Match Statements 497
Attribute Modification 498
Common Route Policy Structure 499
Boolean Operators 504
Negation 504
Conjunction 504
Disjunction 505
Order of Processing 505
Comparing Prefix Sets to Prefix Lists 506
Parameterization 507
Route Policy Nesting 510
Original Value 511
Editors 512
RPL Examples 513
RPL Verification 515
Redistribution RPL Verification 516
BGP RPL Verification 517
References in This Chapter 519
Chapter 12 Advanced Route Manipulation 521
Conditional Routing of Packets 521
Policy-Based Routing Configuration 522
Access-List-Based Forwarding Configuration 523
Local PBR 525
Administrative Distance 526
Modifying EIGRP AD 528
Modifying OSPF AD 529
Modifying IS-IS AD 531
Modifying BGP AD 532
Route Filtering and Manipulation 534
EIGRP Filtering by Prefix 534
EIGRP Filtering by Hop Count 538
EIGRP Offset Lists 538
OSPF Filtering (Local) 541
OSPF Filtering (Area) 543
IS-IS Filtering (Local) 546
BGP Filtering 546
Clearing BGP Connections 549
Summary 550
References in This Chapter 550
Chapter 13 Route Redistribution 551
Redistribution Basics 553
Redistribution Is Not Transitive 553
Sequential Protocol Redistribution 555
Routes Must Exist in the RIB 555
Metrics 558
Protocol-Specific Configuration 558
Source-Specific Behaviors 560
Connected Networks 561
IS-IS 561
BGP 562
Destination-Specific Behaviors 563
EIGRP 563
OSPF 568
IS-IS 576
BGP 580
Challenges with Redistribution 582
Route Feedback 583
Suboptimal Routing 584
Invalid Routing Tables 589
Routing Loops 590
Methods to Avoid Routing Loops 593
Prefix Filtering 593
Tagging 595
Increase Seed Metrics 598
Administrative Distance 601
Summarization on Redistributing Router 603
Solutions to Redistribution Challenges 606
Summary 606
References in This Chapter 607
Part IV Advanced BGP
Chapter 14 Advanced BGP 609
BGP Communities 609
Enabling BGP Community Support 610
Well-Known Communities 611
Internet 611
No_Export 611
No_Advertise 614
No_Export_SubConfed 617
Conditionally Matching BGP Communities 620
Community Set 621
Inline 622
Setting Private BGP Communities 625
Route Summarization 628
Aggregate Address 629
Flexible Route Suppression 632
Selective Prefix Suppression 632
Leaking Suppressed Routes 634
Atomic Aggregate 637
Route Aggregation with AS_SET 639
Route Aggregation with Selective Advertisement of AS_Set 641
Default Route Advertisement 643
Default Route Advertisement Per Neighbor 644
Conditional Route Advertisement 645
Outbound Route Filtering 647
Backdoor Networks 649
Maximum Autonomous System 652
Maximum Prefix 654
Remove Private Autonomous System 656
Allow Autonomous System 658
Local Autonomous System 660
Configuration Scalability 664
IOS Peer Groups 664
IOS Peer Templates 665
IOS XR Configuration Templates 667
Summary 668
References in This Chapter 669
Chapter 15 BGP Best Path Selection 671
BGP Best Path Overview 672
Weight 673
Local Preference 679
Locally Originated via Network or Aggregate Advertisement 684
Accumulated Interior Gateway Protocol 686
Shortest AS_Path 694
Origin Type 700
Multi-Exit Discriminator 704
Missing MED behavior 709
Always Compare Med 711
BGP Deterministic MED 713
eBGP over iBGP 714
Lowest IGP Metric 718
Prefer the Oldest EBGP Path 720
Router ID 720
Minimum Cluster List Length 721
Lowest Neighbor Address 722
BGP ECMP 723
eBGP and iBGP Multipath 723
eiBGP Multipath 726
R1 729
R2 730
XR3 730
XR4 730
XR5 731
AS_Path Relax 731
Suboptimal Routing with Route Reflectors 733
Additional Route Reflector 734
Shadow Route Reflector 735
Shadow Session Route Reflector 738
BGP Add-Path 739
Summary 742
Further Reading 743
Part V Multicast
Chapter 16 IPv4 Multicast Routing 745
Multicast Fundamentals 745
Multicast Addressing 749
Layer 2 Multicast Addresses 752
Internet Group Management Protocol 753
IGMP Snooping 753
IGMPv2 756
IGMPv3 759
Multicast Distribution Trees 759
Source Trees 759
Shared Trees 760
Protocol Independent Multicast 762
PIM Dense Mode 765
PIM Sparse Mode 768
PIM Shared and Source Path Trees 768
Shared Tree Join 769
Source Registration 769
PIM SPT Switchover 771
Designated Routers 772
Rendezvous Points 772
Static RP 773
Auto-RP 773
Candidate RPs 773
RP Mapping Agents 774
PIM Bootstrap Router 775
Candidate RPs 775
Reverse Path Forwarding 776
PIM Forwarder 778
Basic Multicast Configuration 780
Configure Rendezvous Points 783
Static RP 784
Auto-RP 785
BSR 786
Multicast Verification 787
Bidirectional PIM 802
Bidir-PIM Designated Forwarder 804
Summary 808
References in This Chapter 809
Chapter 17 Advanced IPv4 Multicast Routing 811
Interdomain Multicast Routing 811
Multiprotocol BGP 812
Multicast Source Discovery Protocol 817
MSDP Source Active Message Types 818
SA Messages 819
Keepalive Messages 819
MSDP Peers 822
MSDP Verification 828
MSDP Stub Networks 831
Rendezvous Point Redundancy 833
Auto-RP with Multiple RPs 835
Auto-RP Group Filtering 836
BSR with Multiple RPs 840
BSR Group Filtering 843
BSR RP Hash Algorithm 845
Static RP with Multiple RPs 846
Anycast RP 847
Source Specific Multicast 850
SSM Mapping 857
DNS SSM Mapping 857
Static SSM Mapping 860
Multicast Security 862
Auto-RP Scoping 862
Multicast Boundaries 863
Administratively Scoped Boundaries 863
Auto-RP Multicast Boundaries 865
BSR Multicast Boundaries 866
Auto-RP Cisco-RP-Announce Message Filtering 867
PIM-SM Source Registration Filtering 867
PIM-SM Accept RP 868
PIM Neighbor Control 869
PIM Register Rate Limit 870
Multicast Traffic Engineering 871
RPF Rules 871
Static Mroutes 872
MBGP 875
Static IGMP Joins 882
Multicast Troubleshooting 886
Mtrace 887
Summary 889
References in This Chapter 891
Part VI IPv6
Chapter 18 IPv6 Addressing 893
IPv6 Address Structure 893
Text Representation Address Abbreviation 895
IPv6 Hexadecimal to Binary Conversion 896
IPv6 Address Types 898
Unicast 898
Global Unicast 900
Unique Local Unicast 904
Link-Local Unicast 905
Anycast 906
Multicast 908
Special IPv6 Addresses 911
Neighbor Discovery Protocol 912
Router, Prefix, and Parameter Discovery. 913
Redirect 919
IPv6 Stateless Address Autoconfiguration 920
Extended Unique Identifier 920
SLAAC Router Configuration 921
RA Options for DNS 923
Stateless DHCPv6 924IOS Stateless DHCPv6 Configuration 924
IOS XR Stateless DHCPv6 Configuration 925
Stateless DHCPv6 Verification 926
Stateful DHCPv6, Relay Agent, and Relay Proxy 926
IOS Relay Agent Configuration 927
IOS Relay Agent Verification 928
IOS XR Proxy Agent Configuration 928
IOS XR Proxy Agent Verification 929
IOS Stateful DHCPv6 Server Configuration 930
IOS XR Stateful DHCPv6 Server Configuration 931
Stateful DHCPv6 Server Verification 932
IPv6 Address Resolution and Neighbor Unreachability Detection 934
Duplicate Address Detection 937
Summary 938
References in This Chapter 939
Chapter 19 IPv6 Routing 941
Static Routing 941
Static Route Configuration 942
Static Route Reference Chart for IPv6 943
EIGRPv6 944
EIGRPv6 Inter-Router Communication 944
EIGRPv6 Configuration 945
IOS EIGRPv6 Autonomous System Configuration (Classic) 945
IOS EIGRPv6 Hierarchical Configuration (Named Mode) 946
IOS XR EIGRPv6 Configuration 946
EIGRPv6 Verification 947
Summarization 950
Default Route 952
Route Filtering 953
EIGRP Configuration Command Reference Chart for IPv6 954
OSPFv3 956
OSPFv3 Inter-Router Communication 957
OSPFv3 Link-State Advertisement 958
OSPFv3 LSA Flooding Scope 959
OSPFv3 Configuration 960
IOS OSPFv3 Configuration 960
IOS XR OSPFv3 Configuration 961
OSPFv3 Verification 962
OSPFv3 Authentication 970
OSPFv3 Multiple Instances 973
OSPFv3 Configuration Command Reference Chart for IPv6 975
Integrated IS-IS for IPv6 977
IS-IS Inter-Router Communication 978
IS-IS Type-Length-Value 978
IS-IS Topology Modes 978
IS-IS Configuration 979
IOS Base Configuration 979
IOS XR Base Configuration 980
IOS Topology Mode Configuration 981
IOS XR Topology Mode Configuration 981
Verification 985
IS-IS Configuration Reference Chart for IPv6 987
Multiprotocol BGP for IPv6 989
Inter-Router Communication 989
BGP Configuration 991
IOS Base Configuration 991
IOS XR Base Configuration 992
BGP Verification 993
IPv6 over IPv4 BGP Sessions 998
BGP Configuration Command Reference Chart for IPv6 1001
IPv6 Route Redistribution 1002
Summary 1006
References in This Chapter 1006
Chapter 20 IPv6 Multicast Routing 1007
IPv6 Multicast Routing Overview 1007
IPv6 Multicast Address Mapping into MAC Address 1009
Enabling Multicast Routing 1010
Multicast Listener Discovery 1010
Protocol Independent Multicast 1015
PIM Sparse Mode 1015
Static RP 1017
Bootstrap Router 1018
Embedded RP 1021
IPv6 Multicast Verification Commands 1024
Reverse Path Forwarding 1030
Multicast Boundary Scope 1032
PIM Source Specific Multicast 1033
Summary 1034
References in This Chapter 1035
Index 1037
Part VII High Availability
Chapter 21 High Availability Online
Appendixes
Appendix A Decimal to Hex to Binary Values Online
Appendix B BGP Attributes Online
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