cisco ios xr routing configuration guide for the cisco crs router

Cisco IOS XR Routing Configuration Guide for the Cisco CRS Router,Release 4.3.x

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Text Part Number: OL-28410-03

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C O N T E N T S

P r e f a c e Preface xxv

Changes to This Document xxv

Obtaining Documentation and Submitting a Service Request xxv

C H A P T E R 1 New and Changed Feature Information in Cisco IOS XR Release 4.3.x 1

New and Changed Routing Features 1

C H A P T E R 2 Implementing BGP 9

Prerequisites for Implementing BGP 12

Information About Implementing BGP 12

BGP Functional Overview 12

BGP Router Identifier 13

BGP Default Limits 13

BGP Next Hop Tracking 14

Next Hop as the IPv6 Address of Peering Interface 15

Scoped IPv4/VPNv4 Table Walk 16

Reordered Address Family Processing 16

New Thread for Next-Hop Processing 16

show, clear, and debug Commands 16

Autonomous System Number Formats in BGP 17

2-byte Autonomous System Number Format 17

4-byte Autonomous System Number Format 17

as-format Command 17

BGP Configuration 17

Configuration Modes 18

Router Configuration Mode 18

Router Address Family Configuration Mode 18

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Neighbor Configuration Mode 18

Neighbor Address Family Configuration Mode 18

VRF Configuration Mode 18

VRF Address Family Configuration Mode 19

VRF Neighbor Configuration Mode 19

VRF Neighbor Address Family Configuration Mode 19

VPNv4 Address Family Configuration Mode 19

VPNv6 Address Family Configuration Mode 19

L2VPN Address Family Configuration Mode 19

Neighbor Submode 20

Configuration Templates 20

Template Inheritance Rules 22

Viewing Inherited Configurations 25

show bgp neighbors 25

show bgp af-group 26

show bgp session-group 28

show bgp neighbor-group 28

No Default Address Family 30

Routing Policy Enforcement 30

Table Policy 32

Update Groups 32

BGP Update Generation and Update Groups 33

BGP Update Group 33

BGP Cost Community 33

How BGP Cost Community Influences the Best Path Selection Process 33

Cost Community Support for Aggregate Routes and Multipaths 34

Influencing Route Preference in a Multiexit IGP Network 36

BGP Cost Community Support for EIGRP MPLS VPN PE-CE with Back-door

Links 36

Adding Routes to the Routing Information Base 38

BGP Best Path Algorithm 38

Comparing Pairs of Paths 38

Order of Comparisons 40

Best Path Change Suppression 41

Administrative Distance 41

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Multiprotocol BGP 43

Route Dampening 45

Minimizing Flapping 46

BGP Routing Domain Confederation 46

BGP Route Reflectors 46

Default Address Family for show Commands 50

MPLS VPN Carrier Supporting Carrier 50

BGP Keychains 51

BGP Nonstop Routing 51

BGP Best-External Path 53

BGP Prefix Independent Convergence Unipath Primary/Backup 54

BGP Local Label Retention 54

BGP Over GRE Interfaces 55

Command Line Interface (CLI) Consistency for BGP Commands 55

BGP Additional Paths 55

iBGP Multipath Load Sharing 55

Accumulated Interior Gateway Protocol Attribute 56

Per VRF and Per CE Label for IPv6 Provider Edge 56

Constrained Route Distribution for BGP/MPLS Internet Protocol VPNs 57

Constrained Route Distribution Benefits 57

BGP RT-constrain SAFIrt-filter 57

Selective VRF Download 58

Line Card Roles and Filters in Selective VRF Download 58

BGP Accept Own 59

BGP DMZ Link Bandwidth for Unequal Cost Recursive Load Balancing 61

BFD Multihop Support for BGP 61

BGP Multi-Instance/Multi-AS Support 61

BGP Prefix Origin Validation Based on RPKI 62

BGP 3107 PIC Updates for Global Prefixes 62

BGP Prefix Independent Convergence for RIB and FIB 63

BGP Update Message Error Handling 63

BGP Attribute Filtering 63

BGP Attribute Filter Actions 64

BGP Error Handling and Attribute Filtering Syslog Messages 64

BGP VRF Dynamic Route Leaking 65

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How to Implement BGP 65

Enabling BGP Routing 65

Configuring a Routing Domain Confederation for BGP 68

Resetting an eBGP Session Immediately Upon Link Failure 70

Logging Neighbor Changes 70

Adjusting BGP Timers 70

Changing the BGP Default Local Preference Value 72

Configuring the MED Metric for BGP 73

Configuring BGP Weights 74

Tuning the BGP Best-Path Calculation 75

Indicating BGP Back-door Routes 77

Configuring Aggregate Addresses 78

Redistributing iBGP Routes into IGP 80

Redistributing Prefixes into Multiprotocol BGP 81

Configuring BGP Route Dampening 83

Applying Policy When Updating the Routing Table 88

Setting BGP Administrative Distance 90

Configuring a BGP Neighbor Group and Neighbors 91

Configuring a Route Reflector for BGP 94

Configuring BGP Route Filtering by Route Policy 96

Configuring BGP Next-Hop Trigger Delay 98

Disabling Next-Hop Processing on BGP Updates 99

Configuring BGP Community and Extended-Community Advertisements 100

Configuring the BGP Cost Community 103

Configuring Software to Store Updates from a Neighbor 107

Configuring a VPN Routing and Forwarding Instance in BGP 109

Defining Virtual Routing and Forwarding Tables in Provider Edge Routers 109

Configuring the Route Distinguisher 111

Configuring BGP to Advertise VRF Routes for Multicast VPN from PE to PE 113

Advertising VRF Routes for MVPNv4 from PE to PE 114

Advertising VRF Routes for MVPNv6 from PE to PE 119

Configuring PE-PE or PE-RR Interior BGP Sessions 124

Configuring Route Reflector to Hold Routes That Have a Defined Set of RT

Communities 126

Configuring BGP as a PE-CE Protocol 128

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Redistribution of IGPs to BGP 132

Configuring Keychains for BGP 134

Configuring an MDT Address Family Session in BGP 136

Disabling a BGP Neighbor 140

Resetting Neighbors Using BGP Inbound Soft Reset 141

Resetting Neighbors Using BGP Outbound Soft Reset 142

Resetting Neighbors Using BGP Hard Reset 143

Clearing Caches, Tables, and Databases 144

Displaying System and Network Statistics 145

Displaying BGP Process Information 147

Monitoring BGP Update Groups 148

Configuring BGP Nonstop Routing 149

Configuring Best-External Path Advertisement 150

Installing Primary Backup Path for Prefix Independent Convergence (PIC) 152

Retaining Allocated Local Label for Primary Path 153

Configuring BGP Additional Paths 155

Configuring iBGP Multipath Load Sharing 157

Originating Prefixes with AiGP 158

Configuring BGP Accept Own 160

Enabling BGP Unequal Cost Recursive Load Balancing 161

Configuring RPKI Cache-server 163

Configuring RPKI Prefix Validation 166

Configuring RPKI Bestpath Computation 168

Configuring VRF Dynamic Route Leaking 169

Configuration Examples for Implementing BGP 171

Enabling BGP: Example 171

Displaying BGP Update Groups: Example 173

BGP Neighbor Configuration: Example 173

BGP Confederation: Example 174

BGP Route Reflector: Example 176

BGP MDT Address Family Configuration: Example 176

BGP Nonstop Routing Configuration: Example 176

Best-External Path Advertisement Configuration: Example 177

Primary Backup Path Installation: Example 177

Allocated Local Label Retention: Example 177

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iBGP Multipath Loadsharing Configuration: Example 177

Originating Prefixes With AiGP: Example 177

BGP Accept Own Configuration: Example 178

BGP Unequal Cost Recursive Load Balancing: Example 179

VRF Dynamic Route Leaking Configuration: Example 181

Where to Go Next 181

Additional References 181

C H A P T E R 3 Implementing BFD 185

Prerequisites for Implementing BFD 188

Restrictions for Implementing BFD 188

Information About BFD 189

Differences in BFD in Cisco IOS XR Software and Cisco IOS Software 189

BFD Modes of Operation 190

BFD Packet Information 191

BFD Source and Destination Ports 191

BFD Packet Intervals and Failure Detection 191

BFD Packet Intervals on Physical Interfaces 191

BFD Packet Intervals on Bundle Member Links 192

Control Packet Failure Detection In Asynchronous Mode 192

Echo Packet Failure Detection In Asynchronous Mode 192

Echo Failure Detection Examples 193

Summary of Packet Intervals and Failure Detection Times for BFD on Bundle

Interfaces 194

Echo Packet Latency 195

Priority Settings for BFD Packets 195

BFD for IPv4 196

BFD for IPv6 197

BFD on Bundled VLANs 197

BFD Over Member Links on Link Bundles 199

Overview of BFD State Change Behavior on Member Links and Bundle Status 199

BFD Multipath Sessions 201

BFD for MultiHop Paths 201

Setting up BFD Multihop 202

Limitations of BFD 202

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Bidirectional Forwarding Detection over Logical Bundle 202

BFD IPv6 Multihop 202

BFD over MPLS Traffic Engineering LSPs 203

BFD over Satellite Interfaces 204

Limitations 204

How to Configure BFD 204

BFD Configuration Guidelines 204

Configuring BFD Under a Dynamic Routing Protocol or Using a Static Route 205

Enabling BFD on a BGP Neighbor 205

Enabling BFD for OSPF on an Interface 207

Enabling BFD for OSPFv3 on an Interface 209

Enabling BFD on a Static Route 210

Configuring BFD on Bundle Member Links 212

Prerequisites for Configuring BFD on Bundle Menmber Links 212

Specifying the BFD Destination Address on a Bundle 212

Enabling BFD Sessions on Bundle Members 213

Configuring the Minimum Thresholds for Maintaining an Active Bundle 214

Configuring BFD Packet Transmission Intervals and Failure Detection Times on a

Bundle 216

Configuring Allowable Delays for BFD State Change Notifications Using Timers on a

Bundle 217

Enabling Echo Mode to Test the Forwarding Path to a BFD Peer 219

Overriding the Default Echo Packet Source Address 219

Specifying the Echo Packet Source Address Globally for BFD 219

Specifying the Echo Packet Source Address on an Individual Interface or Bundle 220

Configuring BFD Session Teardown Based on Echo Latency Detection 222

Delaying BFD Session Startup Until Verification of Echo Path and Latency 223

Disabling Echo Mode 224

Disabling Echo Mode on a Router 225

Disabling Echo Mode on an Individual Interface or Bundle 226

Minimizing BFD Session Flapping Using BFD Dampening 227

Enabling and Disabling IPv6 Checksum Support 228

Enabling and Disabling IPv6 Checksum Calculations for BFD on a Router 228

Enabling and Disabling IPv6 Checksum Calculations for BFD on an Individual Interface

or Bundle 229

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Clearing and Displaying BFD Counters 231

Configuring Coexistence Between BFD over Bundle (BoB) and BFD over Logical Bundle

(BLB) 231

Configuring BFD over MPLS Traffic Engineering LSPs 233

Enabling BFD Parameters for BFD over TE Tunnels 233

Configuring BFD Bring up Timeout 234

Configuring BFD Dampening for TE Tunnels 235

Configuring Periodic LSP Ping Requests 237

Configuring BFD at the Tail End 238

Configuring BFD over LSP Sessions on Line Cards 239

Configuration Examples for Configuring BFD 241

BFD Over BGP: Example 241

BFD Over OSPF: Examples 241

BFD Over Static Routes: Examples 242

BFD on Bundled VLANs: Example 242

BFD on Bundle Member Links: Examples 243

Echo Packet Source Address: Examples 244

Echo Latency Detection: Examples 245

Echo Startup Validation: Examples 245

BFD Echo Mode Disable: Examples 246

BFD Dampening: Examples 246

BFD IPv6 Checksum: Examples 246

BFD Peers on Routers Running Cisco IOS and Cisco IOS XR Software: Example 247

BFD over MPLS TE LSPs: Examples 247

BFD over MPLS TE Tunnel Head-end Configuration: Example 248

BFD over MPLS TE Tunnel Tail-end Configuration: Example 248



Related Documents 249

Standards 249

RFCs 249

MIBs 249

Technical Assistance 250

C H A P T E R 4 Implementing EIGRP 251

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Prerequisites for Implementing EIGRP 252

Restrictions for Implementing EIGRP 252

Information About Implementing EIGRP 252

EIGRP Functional Overview 253

EIGRP Features 253

EIGRP Components 253

EIGRP Configuration Grouping 254

EIGRP Configuration Modes 255

EIGRP Interfaces 256

Redistribution for an EIGRP Process 256

Metric Weights for EIGRP Routing 256

Mismatched K Values 257

Goodbye Message 257

Percentage of Link Bandwidth Used for EIGRP Packets 258

Floating Summary Routes for an EIGRP Process 258

Split Horizon for an EIGRP Process 260

Adjustment of Hello Interval and Hold Time for an EIGRP Process 261

Stub Routing for an EIGRP Process 261

Route Policy Options for an EIGRP Process 262

EIGRP Layer 3 VPN PE-CE Site-of-Origin 263

Router Interoperation with the Site-of-Origin Extended Community 263

IPv6 and IPv6 VPN Provider Edge Support over MPLS and IP 264

EIGRP v4/v6 Authentication Using Keychain 264

EIGRP Wide Metric Computation 264

How to Implement EIGRP 265

Enabling EIGRP Routing 265

Configuring Route Summarization for an EIGRP Process 267

Redistributing Routes for EIGRP 269

Creating a Route Policy and Attaching It to an EIGRP Process 271

Configuring Stub Routing for an EIGRP Process 273

Configuring EIGRP as a PE-CE Protocol 275

Redistributing BGP Routes into EIGRP 277

Monitoring EIGRP Routing 279

Configuring an EIGRP Authentication Keychain 281

Configuring an Authentication Keychain for an IPv4/IPv6 Interface on a Default VRF 281

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Configuring an Authentication Keychain for an IPv4/IPv6 Interface on a Nondefault

VRF 283

Configuration Examples for Implementing EIGRP 284

Configuring a Basic EIGRP Configuration: Example 284

Configuring an EIGRP Stub Operation: Example 285

Configuring an EIGRP PE-CE Configuration with Prefix-Limits: Example 285

Configuring an EIGRP Authentication Keychain: Example 286


C H A P T E R 5 Implementing IS-IS 289

Prerequisites for Implementing IS-IS 291

Restrictions for Implementing IS-IS 291

Information About Implementing IS-IS 291

IS-IS Functional Overview 291

Key Features Supported in the Cisco IOS XR IS-IS Implementation 291

IS-IS Configuration Grouping 292

IS-IS Configuration Modes 292

Router Configuration Mode 292

Router Address Family Configuration Mode 292

Interface Configuration Mode 293

Interface Address Family Configuration Mode 293

IS-IS Interfaces 293

Multitopology Configuration 293

IPv6 Routing and Configuring IPv6 Addressing 294

Limit LSP Flooding 294

Flood Blocking on Specific Interfaces 294

Mesh Group Configuration 294

Maximum LSP Lifetime and Refresh Interval 295

Single-Topology IPv6 Support 295

Multitopology IPv6 Support 295

IS-IS Authentication 295

Nonstop Forwarding 296

Multi-Instance IS-IS 297

Multiprotocol Label Switching Traffic Engineering 297

Overload Bit on Router 297

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Overload Bit Configuration During Multitopology Operation 298

IS-IS Overload Bit Avoidance 298

Default Routes 298

Attached Bit on an IS-IS Instance 298

IS-IS Support for Route Tags 299

Multicast-Intact Feature 299

Multicast Topology Support Using IS-IS 299

MPLS Label Distribution Protocol IGP Synchronization 300

MPLS LDP-IGP Synchronization Compatibility with LDP Graceful Restart 300

MPLS LDP-IGP Synchronization Compatibility with IGP Nonstop Forwarding 300

Label Distribution Protocol IGP Auto-configuration 301

MPLS TE Forwarding Adjacency 301

MPLS TE Interarea Tunnels 301

IP Fast Reroute 301

IS-IS Over GRE Interfaces 302

Unequal Cost Multipath Load-balancing for IS-IS 302

How to Implement IS-IS 302

Enabling IS-IS and Configuring Level 1 or Level 2 Routing 303

Configuring Single Topology for IS-IS 305

Configuring Multitopology Routing 309

Restrictions for Configuring Multitopology Routing 309

Information About Multitopology Routing 310

Configuring a Global Topology and Associating It with an Interface 310

Enabling an IS-IS Topology 311

Placing an Interface in a Topology in IS-IS 313

Configuring a Routing Policy 314

Configuring Multitopology for IS-IS 315

Controlling LSP Flooding for IS-IS 316

Configuring Nonstop Forwarding for IS-IS 320

Configuring Authentication for IS-IS 322

Configuring Keychains for IS-IS 323

Configuring MPLS Traffic Engineering for IS-IS 325

Tuning Adjacencies for IS-IS 327

Setting SPF Interval for a Single-Topology IPv4 and IPv6 Configuration 330

Customizing Routes for IS-IS 332

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Configuring MPLS LDP IS-IS Synchronization 335

Enabling Multicast-Intact 337

Tagging IS-IS Interface Routes 338

Setting the Priority for Adding Prefixes to the RIB 340

Configuring IP/LDP Fast Reroute 341

Configuring IS-IS Overload Bit Avoidance 344

Configuration Examples for Implementing IS-IS 345

Configuring Single-Topology IS-IS for IPv6: Example 345

Configuring Multitopology IS-IS for IPv6: Example 345

Redistributing IS-IS Routes Between Multiple Instances: Example 346

Tagging Routes: Example 346

Configuring IS-IS Overload Bit Avoidance: Example 347



C H A P T E R 6 Implementing OSPF 351

Prerequisites for Implementing OSPF 353

Information About Implementing OSPF 354

OSPF Functional Overview 354

Key Features Supported in the Cisco IOS XR Software OSPF Implementation 355

Comparison of Cisco IOS XR Software OSPFv3 and OSPFv2 356

OSPF Hierarchical CLI and CLI Inheritance 356

OSPF Routing Components 357

Autonomous Systems 357

Areas 357

Backbone Area 358

Stub Area 358

Not-so-Stubby Area 358

Routers 358

Area Border Routers 358

Autonomous System Boundary Routers (ASBR) 359

Interior Routers 359

OSPF Process and Router ID 359

Supported OSPF Network Types 360

Route Authentication Methods for OSPF 360

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Plain Text Authentication 360

MD5 Authentication 360

Authentication Strategies 361

Key Rollover 361

Neighbors and Adjacency for OSPF 361

Designated Router (DR) for OSPF 361

Default Route for OSPF 362

Link-State Advertisement Types for OSPF Version 2 362

Link-State Advertisement Types for OSPFv3 363

Virtual Link and Transit Area for OSPF 364

OSPFv2 Sham Link Support for MPLS VPN 364

OSPF SPF Prefix Prioritization 366

Route Redistribution for OSPF 368

OSPF Shortest Path First Throttling 368

Nonstop Forwarding for OSPF Version 2 369

Graceful Restart for OSPFv3 369

Modes of Graceful Restart Operation 370

Restart Mode 370

Helper Mode 370

Graceful Restart Requirements and Restrictions 371

Warm Standby and Nonstop Routing for OSPF Version 2 372

Warm Standby for OSPF Version 3 372

Multicast-Intact Support for OSPF 372

Load Balancing in OSPF Version 2 and OSPFv3 373

Multi-Area Adjacency for OSPF Version 2 373

Label Distribution Protocol IGP Auto-configuration for OSPF 374

OSPF Authentication Message Digest Management 374

GTSM TTL Security Mechanism for OSPF 375

Path Computation Element for OSPFv2 375

OSPF Queue Tuning Parameters 375

OSPF IP Fast Reroute Loop Free Alternate 376

OSPF Over GRE Interfaces 376

Management Information Base (MIB) for OSPFv3 376

VRF-lite Support for OSPFv2 376

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OSPFv3 Timers Link-state Advertisements and Shortest Path First Throttle Default Values

Update 377

How to Implement OSPF 377

Enabling OSPF 377

Configuring Stub and Not-So-Stubby Area Types 379

Configuring Neighbors for Nonbroadcast Networks 382

Configuring Authentication at Different Hierarchical Levels for OSPF Version 2 387

Controlling the Frequency That the Same LSA Is Originated or Accepted for OSPF 390

Creating a Virtual Link with MD5 Authentication to Area 0 for OSPF 392

Examples 397

Summarizing Subnetwork LSAs on an OSPF ABR 397

Redistributing Routes from One IGP into OSPF 399

Configuring OSPF Shortest Path First Throttling 402

Examples 404

Configuring Nonstop Forwarding Specific to Cisco for OSPF Version 2 405

Configuring OSPF Version 2 for MPLS Traffic Engineering 407

Examples 409

Configuring OSPFv3 Graceful Restart 411

Displaying Information About Graceful Restart 413

Configuring an OSPFv2 Sham Link 414

Enabling Nonstop Routing for OSPFv2 417

Enabling Nonstop Routing for OSPFv3 418

Configuring OSPF SPF Prefix Prioritization 419

Enabling Multicast-intact for OSPFv2 421

Associating Interfaces to a VRF 422

Configuring OSPF as a Provider Edge to Customer Edge (PE-CE) Protocol 424

Creating Multiple OSPF Instances (OSPF Process and a VRF) 426

Configuring Multi-area Adjacency 428

Configuring Label Distribution Protocol IGP Auto-configuration for OSPF 430

Configuring LDP IGP Synchronization: OSPF 431

Configuring Authentication Message Digest Management for OSPF 432

Examples 434

Configuring Generalized TTL Security Mechanism (GTSM) for OSPF 435

Examples 437

Verifying OSPF Configuration and Operation 438

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Configuring OSPF Queue Tuning Parameters 440

Configuring IP Fast Reroute Loop-free Alternate 441

Enabling IPFRR LFA 441

Excluding an Interface From IP Fast Reroute Per-link Computation 443

Configuration Examples for Implementing OSPF 444

Cisco IOS XR Software for OSPF Version 2 Configuration: Example 444

CLI Inheritance and Precedence for OSPF Version 2: Example 445

MPLS TE for OSPF Version 2: Example 446

ABR with Summarization for OSPFv3: Example 446

ABR Stub Area for OSPFv3: Example 447

ABR Totally Stub Area for OSPFv3: Example 447

Configuring OSPF SPF Prefix Prioritization: Example 447

Route Redistribution for OSPFv3: Example 448

Virtual Link Configured Through Area 1 for OSPFv3: Example 448

Virtual Link Configured with MD5 Authentication for OSPF Version 2: Example 449

VPN Backbone and Sham Link Configured for OSPF Version 2: Example 449

OSPF Queue Tuning Parameters Configuration: Example 451



C H A P T E R 7 Implementing and Monitoring RIB 455

Prerequisites for Implementing RIB 456

Information About RIB Configuration 456

Overview of RIB 456

RIB Data Structures in BGP and Other Protocols 457

RIB Administrative Distance 457

RIB Support for IPv4 and IPv6 458

RIB Statistics 458

IPv6 Provider Edge IPv6 and IPv6 VPN Provider Edge Transport over MPLS 458

IP Fast Reroute 459

RIB Quarantining 459

Route and Label Consistency Checker (RCC and LCC) 459

How to Deploy and Monitor RIB 460

Verifying RIB Configuration Using the Routing Table 460

Verifying Networking and Routing Problems 461

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Disabling RIB Next-hop Dampening 462

Configuring RCC and LCC 463

Enabling RCC and LCC On-demand Scan 463

Enabling RCC and LCC Background Scan 464

Configuration Examples for RIB Monitoring 466

Output of show route Command: Example 466

Output of show route backup Command: Example 467

Output of show route best-local Command: Example 467

Output of show route connected Command: Example 467

Output of show route local Command: Example 467

Output of show route longer-prefixes Command: Example 468

Output of show route next-hop Command: Example 468

Enabling RCC and LCC: Example 468



C H A P T E R 8 Implementing RIP 471

Prerequisites for Implementing RIP 472

Information About Implementing RIP 472

RIP Functional Overview 472

Split Horizon for RIP 473

Route Timers for RIP 473

Route Redistribution for RIP 473

Default Administrative Distances for RIP 474

Routing Policy Options for RIP 475

Authentication Using Keychain in RIP 475

In-bound RIP Traffic on an Interface 476

Out-bound RIP Traffic on an Interface 477

How to Implement RIP 477

Enabling RIP 477

Customizing RIP 479

Control Routing Information 481

Creating a Route Policy for RIP 483

Configuring RIP Authentication Keychain 485

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Configuring RIP Authentication Keychain for IPv4 Interface on a Non-default VRF 485

Configuring RIP Authentication Keychain for IPv4 Interface on Default VRF 487

Configuration Examples for Implementing RIP 489

Configuring a Basic RIP Configuration: Example 489

Configuring RIP on the Provider Edge: Example 489

Adjusting RIP Timers for each VRF Instance: Example 490

Configuring Redistribution for RIP: Example 490

Configuring Route Policies for RIP: Example 491

Configuring Passive Interfaces and Explicit Neighbors for RIP: Example 491

Controlling RIP Routes: Example 492

Configuring RIP Authentication Keychain: Example 492


C H A P T E R 9 Implementing Routing Policy 495

Prerequisites for Implementing Routing Policy 497

Restrictions for Implementing Routing Policy 497

Information About Implementing Routing Policy 497

Routing Policy Language 497

Routing Policy Language Overview 498

Routing Policy Language Structure 498

Names 498

Sets 499

as-path-set 500

community-set 501

extcommunity-set 501

prefix-set 504

Enhanced Prefix-length Manipulation 505

rd-set 506

Routing Policy Language Components 506

Routing Policy Language Usage 507

Routing Policy Configuration Basics 509

Policy Definitions 509

Parameterization 510

Parameterization at Attach Points 511

Global Parameterization 511

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Semantics of Policy Application 512

Boolean Operator Precedence 512

Multiple Modifications of the Same Attribute 512

When Attributes Are Modified 513

Default Drop Disposition 513

Control Flow 514

Policy Verification 514

Range Checking 515

Incomplete Policy and Set References 515

Attached Policy Modification 515

Verification of Attribute Comparisons and Actions 516

Policy Statements 516

Remark 516

Disposition 516

Action 518

If 518

Boolean Conditions 520

apply 521

Attach Points 521

BGP Policy Attach Points 522

Additional-Path 522

Aggregation 522

Dampening 523

Default Originate 523

Neighbor Export 524

Neighbor Import 524

Network 525

Redistribute 525

Show BGP 526

Table Policy 527

Import 527

Export 528

Retain Route-Target 529

Label-Mode 529

Allocate-Label 530

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Neighbor-ORF 530

Next-hop 531

Clear-Policy 531

Debug 532

BGP Attributes and Operators 532

OSPF Policy Attach Points 548

Default-Information Originate 548

Redistribute 548

Area-in 549

Area-out 549

SPF Prefix-priority 550

OSPF Attributes and Operators 550

Distribute-list in 551

OSPFv3 Policy Attach Points 552


Redistribute 552

OSPFv3 Attributes and Operators 553

IS-IS Policy Attach Points 553

Redistribute 553


Inter-area-propagate 554

IS-IS Attributes and Operators 555

EIGRP Policy Attach Points 555

Default-Accept-In 556

Default-Accept-Out 556

Policy-In 556

Policy-Out 557

If-Policy-In 557

If-Policy-Out 557

Redistribute 557

EIGRP Attributes and Operators 558

RIP Policy Attach Points 559


Redistribute 559

Global-Inbound 560

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Contents

Global-Outbound 560

Interface-Inbound 560

Interface-Outbound 560

RIP Attributes and Operators 560

PIM Policy Attach Points 562

rpf-topology 562

PIM Attributes and Operators 563

Attached Policy Modification 563

Nonattached Policy Modification 563

Editing Routing Policy Configuration Elements 564

Editing Routing Policy Configuration Elements Using the Nano Editor 564

Editing Routing Policy Configuration Elements Using the Emacs Editor 564

Editing Routing Policy Configuration Elements Using the Vim Editor 565

Editing Routing Policy Configuration Elements Using the CLI 566

Editing Routing Policy Language set elements Using XML 566

Hierarchical Policy Conditions 566

Apply Condition Policies 566

Behavior of pass/drop/done RPL Statements for Simple Hierarchical Policies 567

Behavior of pass/drop/done RPL Statements for Hierarchical Policy

Conditions 568

Nested Wildcard Apply Policy 569

VRF Import Policy Enhancement 569

Flexible L3VPN Label Allocation Mode 570

How to Implement Routing Policy 570

Defining a Route Policy 570

Attaching a Routing Policy to a BGP Neighbor 571

Modifying a Routing Policy Using a Text Editor 573

Configuration Examples for Implementing Routing Policy 574

Routing Policy Definition: Example 574

Simple Inbound Policy: Example 574

Modular Inbound Policy: Example 575

Translating Cisco IOS Route Maps to Cisco IOS XR Routing Policy Language:

Example 576


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C H A P T E R 1 0 Implementing Static Routes 579

Prerequisites for Implementing Static Routes 580

Restrictions for Implementing Static Routes 580

Information About Implementing Static Routes 580

Static Route Functional Overview 580

Default Administrative Distance 581

Directly Connected Routes 581

Recursive Static Routes 582

Fully Specified Static Routes 582

Floating Static Routes 583

Default VRF 583

IPv4 and IPv6 Static VRF Routes 583

How to Implement Static Routes 583

Configuring a Static Route 583

Configuring a Static Route Under Multicast SAFI 585

Configuring a Floating Static Route 587

Configuring Static Routes Between PE-CE Routers 588

Changing the Maximum Number of Allowable Static Routes 589

Associating a VRF with a Static Route 591

Configuration Examples 592

Configuring Traffic Discard: Example 592

Configuring a Fixed Default Route: Example 593

Configuring a Floating Static Route: Example 593

Configuring a Static Route Between PE-CE Routers: Example 593



C H A P T E R 1 1 Implementing RCMD 597

Route Convergence Monitoring and Diagnostics 597

Configuring Route Convergence Monitoring and Diagnostics 598

Route Convergence Monitoring and Diagnostics Prefix Monitoring 601

Route Convergence Monitoring and Diagnostics OSPF Type 3/5/7 Link-state Advertisements

Monitoring 601

Enabling RCMD Monitoring for IS-IS Prefixes 601

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Enabling RCMD Monitoring for OSPF Prefixes 603

Enabling RCMD Monitoring for Type 3/5/7 OSPF LSAs 604

Enabling RCMD Monitoring for IS-IS Prefixes: Example 605

Enabling RCMD Monitoring for OSPF Prefixes: Example 605

Enabling RCMD Monitoring for Type 3/5/7 OSPF LSAs: Example 606

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Preface

The Cisco IOS XR Routing Configuration Guide for the Cisco CRS Router preface contains these sections:

Changes to This Document, page xxv

Obtaining Documentation and Submitting a Service Request, page xxv

Changes to This DocumentThis table lists the technical changes made to this document since it was first published.

Table 1: Changes to This Document

Change SummaryDateRevision

Republished with documentationupdates for Cisco IOS XR Release4.3.2 features.

September 2013OL-28410-03

Republished with documentationupdates for Cisco IOS XR Release4.3.1 features.

May, 2013OL-28410-02

Initial release of this document.December, 2012OL-28410-01

Obtaining Documentation and Submitting a Service RequestFor information on obtaining documentation, using the Cisco Bug Search Tool (BST), submitting a servicerequest, and gathering additional information, seeWhat's New in Cisco Product Documentation, at: http://www.cisco.com/en/US/docs/general/whatsnew/whatsnew.html.

Subscribe toWhat's New in Cisco Product Documentation, which lists all new and revised Cisco technicaldocumentation, as an RSS feed and deliver content directly to your desktop using a reader application. TheRSS feeds are a free service.

Cisco IOS XR Routing Configuration Guide for the Cisco CRS Router, Release 4.3.x OL-28410-03 xxv

Cisco IOS XR Routing Configuration Guide for the Cisco CRS Router, Release 4.3.xxxvi OL-28410-03

PrefaceObtaining Documentation and Submitting a Service Request

C H A P T E R 1New and Changed Feature Information in CiscoIOS XR Release 4.3.x

This table summarizes the new and changed feature information for the Cisco IOS XR Routing ConfigurationGuide for the Cisco CRS Router, and tells you where they are documented.

For a complete list of new and changed features in Cisco IOS XR Software, Release 4.3.x, see the New andChanged Features in Cisco IOS XR Software, Release 4.3.x for Cisco CRS Router document.

New and Changed Routing Features, page 1

New and Changed Routing FeaturesWhere DocumentedIntroduced/Changed in ReleaseDescriptionFeature

Implementing BFD chapter.

BFD over Satellite Interfaces,on page 204

Refer BFD Commands chapterin Cisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for configuring BFD overSatellite Interface.

Release 4.3.2This feature was introduced.BFD over Satellite Interface

Cisco IOS XR Routing Configuration Guide for the Cisco CRS Router, Release 4.3.x OL-28410-03 1

Where DocumentedIntroduced/Changed in ReleaseDescriptionFeature

Implementing BGP chapter

BGPVRFDynamicRouteLeaking, on page 65

Configuring VRFDynamic Route Leaking,on page 169

VRF Dynamic RouteLeaking Configuration:Example, on page 181

Refer BGP Commands chapterin Cisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for configuring VRFDynamic Route Leaking.

Release 4.3.1This feature was introduced.BGP VRF Dynamic RouteLeaking

Implementing BidirectionalForwarding Detection chapter.

BFD IPv6 Multihop, on page202

ReferBidirectional ForwardingDetection Commands chapterin Cisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for configuring BFD IPv6Multihop.

Release 4.3.1This feature was introduced.BFD IPv6 Multihop

Cisco IOS XR Routing Configuration Guide for the Cisco CRS Router, Release 4.3.x2 OL-28410-03

New and Changed Feature Information in Cisco IOS XR Release 4.3.xNew and Changed Routing Features


Implementing BidirectionalForwarding Detection chapter.

BFD over MPLS TrafficEngineering LSPs, onpage 203

Enabling BFDParametersfor BFD over TETunnels, on page 233

Configuring BFD Bringup Timeout, on page 234

Configuring BFDDampening for TETunnels, on page 235

Configuring Periodic LSPPing Requests, on page237

Configuring BFD at theTail End, on page 238

Configuring BFD overLSP Sessions on LineCards, on page 239

BFD over MPLS TETunnel Head-endConfiguration: Example,on page 248

BFD over MPLS TETunnel Tail-endConfiguration: Example,on page 248

ReferBidirectional ForwardingDetection Commands chapterin Cisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for configuring BFD overMPLS Traffic EngineeringLSPs.

Release 4.3.1This feature was introduced.BFD over MPLS TrafficEngineering LSPs




Implementing Routing Policychapter.

VRF Import PolicyEnhancement, on page 569

Refer Routing Policy LanguageCommands chapter inCisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for configuring VRF RPLBased Import Policy.

Release 4.3.1This feature was introduced.VRF RPL Based Import Policy

Implementing Routing Policychapter.

Flexible L3VPN LabelAllocationMode, on page570

Label-Mode, on page 529

Refer Routing Policy LanguageCommands chapter inCisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for configuring FlexibleL3VPN Label Allocation.

Release 4.3.1This feature was introduced.Flexible L3VPN LabelAllocation




Implementing RCMD chapter

Route ConvergenceMonitoring andDiagnostics PrefixMonitoring, on page 601

Enabling RCMDMonitoring for IS-ISPrefixes, on page 601

Enabling RCMDMonitoring for IS-ISPrefixes: Example, onpage 605

Enabling RCMDMonitoring for OSPFPrefixes, on page 603

Enabling RCMDMonitoring for OSPFPrefixes: Example, onpage 605

Refer RCMD Commandschapter in Cisco IOS XRRouting Command Referencefor the Cisco CRS Router forinformation on the commandsused for enabling RCMDmonitoring for IS-IS and OSPFprefixes.

Release 4.3.0This feature was introduced.Route ConvergenceMonitoringandDiagnostics (RCMD) PrefixMonitoring




Implementing RCMD chapter

Route ConvergenceMonitoring andDiagnostics OSPF Type3/5/7 Link-stateAdvertisementsMonitoring, on page 601

Enabling RCMDMonitoring for Type 3/5/7OSPF LSAs, on page 604

Enabling RCMDMonitoring for Type 3/5/7OSPF LSAs: Example,on page 606

Refer RCMD Commandschapter in Cisco IOS XRRouting Command Referencefor the Cisco CRS Router forinformation on the commandsused for enabling RCMDmonitoring for type 3/5/7 OSPFLSAs.

Release 4.3.0This feature was introduced.Route ConvergenceMonitoringandDiagnostics (RCMD)OSPFType 3/5/7 LSA Monitoring


Selective VRFDownload, on page 58

Line Card Roles andFilters in Selective VRFDownload, on page 58

Refer BGP Commands chapterin Cisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for disabling selectiveVRF download (SVD)anddisplaying SVD role and stateinformation.

Release 4.3.0This feature was introduced.Selective VRF Download





BGP DMZ LinkBandwidth for UnequalCost Recursive LoadBalancing, on page 61

Enabling BGP UnequalCost Recursive LoadBalancing, on page 161

BGP Unequal CostRecursive LoadBalancing: Example, onpage 179

Refer BGP Commands chapterin Cisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for enabling BGP unequalcost recursive load balancing.

Release 4.3.0This feature was introduced.BGP DMZ Link Bandwidth forUnequal Cost Recursive LoadBalancing

Implementing IS-IS chapter

Unequal Cost MultipathLoad-balancing for IS-IS, onpage 302

Refer IS-IS Commands chapterin Cisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on the commandsused for enabling unequal costmultipath (UCMP) calculationfor IS-IS.

Release 4.3.0This feature was introduced.Unequal Cost MultipathLoad-balancing for IS-IS




Implementing OSPF chapter

VRF-lite Support for OSPFv2,on page 376

ReferOSPFCommands chapterin Cisco IOS XR RoutingCommand Reference for theCisco CRS Router forinformation on capabilityvrf-lite command used forconfiguring VRF-lite capabilityand show ospf command usedto display VRF-liteconfiguration status.

Release 4.3.0This feature was introduced.OSPFv2 VRF-lite

Implementing OSPF chapter

OSPFv3 Timers Link-stateAdvertisements and ShortestPath First Throttle DefaultValues Update, on page 377

Refer OSPFv3 Commandschapter in Cisco IOS XRRouting Command Referencefor the Cisco CRS Routerfortimers throttle lsa all andtimers throttle spf commandreference information.

Release 4.3.0OSPFv3 Timers LSA and SPFThrottle Commands DefaultValues were updated.

OSPFv3 Timers Update

Implementing EIGRP chapter

EIGRP Wide MetricComputation, on page 264

Refer EIGRP Commandschapter in Cisco IOS XRRouting Command Referencefor the Cisco CRS Router forinformation on new andenhanced commands to supportEIGRP wide metriccomputation.

Release 4.3.0Cisco IOS XR EIGRP wasenhanced to support widemetric computation.

EIGRP Wide MetricComputation

Implementing and MonitoringRIB chapter

Flex-LSR Label SwitchProcessor 140

Release 4.3.0This feature was introduced.Flex-LSR Label SwitchProcessor 140



C H A P T E R 2Implementing BGP

Border Gateway Protocol (BGP) is an Exterior Gateway Protocol (EGP) that allows you to create loop-freeinterdomain routing between autonomous systems. An autonomous system is a set of routers under a singletechnical administration. Routers in an autonomous system can use multiple Interior Gateway Protocols(IGPs) to exchange routing information inside the autonomous system and an EGP to route packets outsidethe autonomous system.

This module provides the conceptual and configuration information for BGP on Cisco IOS XR software.

For more information about BGP on the Cisco IOS XR software and complete descriptions of the BGPcommands listed in this module, see Related Documents, on page 181 section of this module. To locatedocumentation for other commands that might appear while performing a configuration task, search onlinein the Cisco IOS XR software master command index.

Note

Feature History for Implementing BGP

ModificationRelease

This feature was introduced.Release 2.0

No modification.Release 3.0

No modification.Release 3.2

VPN routing and forwarding (VRF) support was added, includinginformation on VRF command modes and command syntax.

BGP cost community information was added.

Release 3.3.0

The following features were supported:

Four-byte autonomous system (AS) number

Carrier supporting carrier (CSC) for BGP was added. SeeCisco IOS XR Multiprotocol Label Switching ProtocolConfiguration Guide for information

Key chains

Release 3.4.0


ModificationRelease


IPv6 Provider Edge and IPv6 VPN Provider Edge overMultiprotocol Label Switching

Neighbor-specific VRF IPv6 address family configurations

Address family group-specific VPNv6 configurations

VPN4/VPNv6 over IP core using L2TPv3 tunnels

Multicast Distribution Tree (MDT) Subaddress FamilyIdentifier Information (SAFI) support for multicast VPN(MVPN)

Release 3.5.0

No modification.Release 3.6.0


Advertisement of VRF routes for multicast VPNs (MVPN)for both IPv4 and IPv6 address families from PE to PE

Edits were made to existing MVPN procedures based onnew support for IPv6 multicast VPNs

Procedure Configuring an MDT Address Family Sessionin BGP, on page 136 was updated to reflect MVPNconfiguration of MDT SAFI from PE to PE

Release 3.7.0


Border Gateway Protocol (BGP) nonstop routing (NSR)with stateful switchover (SSO)

Next hop as the IPv6 address of peering interface

Reset weight on import of VPN routes

New commands enforce-first-as andenforce-first-as-disablewere introduced to provide enableand disable configuration options for enforce-first-as featurein Neighbor, Neighbor group, and Session groupconfiguration modes.

Release 3.8.0


Implementing BGP

ModificationRelease


BGP BestExternal Path

BGP Prefix Independent Convergence Unipath PrimaryBackup

BGP Local Label Retention

BGP Over GRE Interfaces

Asplain notation for 4-byte Autonomous System Number

Command Line Interface (CLI) consistency for BGPcommands

L2VPN Address Family Configuration Mode

Release 3.9.0


Accumulated iGP (AiGP)

BGP Add Path Advertisement

iBGP Multipath Load Sharing

Next Hop Self on Route Reflector for iBGP+Label

Release 4.0.0


BGP RT Constrained Route Distribution

Release 4.1.0

The BGP Accept Own feature was added.Release 4.1.1


BGP Multi-Instance/Multi-AS Support

BFD Multihop Support for BGP

BGP Error Handling

Support for Distributed BGP (bgp distributed speaker)configuration was removed.

Release 4.2.0


BGP 3107 PIC Updates for Global Prefixes

BGP Prefix Independent Convergence for RIB and FIB

BGP Prefix Origin Validation Based on RPKI

Release 4.2.1

The BGP Attribute Filtering feature was added.Release 4.2.3


Implementing BGP

ModificationRelease

The BGP DMZ Link Bandwidth for Unequal Cost RecursiveLoad Balancing feature wad added.

Release 4.3.0

The following features were supported

BGP VRF Dynamic Route Leaking

Release 4.3.1

Prerequisites for Implementing BGP, page 12

Information About Implementing BGP, page 12

How to Implement BGP, page 65

Configuration Examples for Implementing BGP, page 171

Where to Go Next, page 181

Additional References, page 181

Prerequisites for Implementing BGPYou must be in a user group associated with a task group that includes the proper task IDs. The commandreference guides include the task IDs required for each command. If you suspect user group assignment ispreventing you from using a command, contact your AAA administrator for assistance.

Information About Implementing BGPTo implement BGP, you need to understand the following concepts:

BGP Functional OverviewBGP uses TCP as its transport protocol. Two BGP routers form a TCP connection between one another (peerrouters) and exchange messages to open and confirm the connection parameters.

BGP routers exchange network reachability information. This information is mainly an indication of the fullpaths (BGP autonomous system numbers) that a route should take to reach the destination network. Thisinformation helps construct a graph that shows which autonomous systems are loop free and where routingpolicies can be applied to enforce restrictions on routing behavior.

Any two routers forming a TCP connection to exchange BGP routing information are called peers or neighbors.BGP peers initially exchange their full BGP routing tables. After this exchange, incremental updates are sentas the routing table changes. BGP keeps a version number of the BGP table, which is the same for all of itsBGP peers. The version number changes whenever BGP updates the table due to routing information changes.Keepalive packets are sent to ensure that the connection is alive between the BGP peers and notificationpackets are sent in response to error or special conditions.


Implementing BGPPrerequisites for Implementing BGP

For information on configuring BGP to distribute Multiprotocol Label Switching (MPLS) Layer 3 virtualprivate network (VPN) information, see the Cisco IOS XRMultiprotocol Label Switching ConfigurationGuide for the Cisco CRS-1 Router.

For information on BGP support for Bidirectional Forwarding Detection (BFD), see the Cisco IOS XRInterface and Hardware Configuration Guide for the Cisco CRS-1 Router and the Cisco IOS XR Interfaceand Hardware Command Reference for the Cisco CRS-1 Router.

Note

BGP Router IdentifierFor BGP sessions between neighbors to be established, BGP must be assigned a router ID. The router ID issent to BGP peers in the OPEN message when a BGP session is established.

BGP attempts to obtain a router ID in the following ways (in order of preference):

By means of the address configured using the bgp router-id command in router configuration mode.

By using the highest IPv4 address on a loopback interface in the system if the router is booted with savedloopback address configuration.

By using the primary IPv4 address of the first loopback address that gets configured if there are not anyin the saved configuration.

If none of these methods for obtaining a router ID succeeds, BGP does not have a router ID and cannot establishany peering sessions with BGP neighbors. In such an instance, an error message is entered in the system log,and the show bgp summary command displays a router ID of 0.0.0.0.

After BGP has obtained a router ID, it continues to use it even if a better router ID becomes available. Thisusage avoids unnecessary flapping for all BGP sessions. However, if the router ID currently in use becomesinvalid (because the interface goes down or its configuration is changed), BGP selects a new router ID (usingthe rules described) and all established peering sessions are reset.

We strongly recommend that the bgp router-id command is configured to prevent unnecessary changesto the router ID (and consequent flapping of BGP sessions).

Note

BGP Default LimitsCisco IOS XRBGP imposes maximum limits on the number of neighbors that can be configured on the routerand on the maximum number of prefixes that are accepted from a peer for a given address family. Thislimitation safeguards the router from resource depletion caused by misconfiguration, either locally or on theremote neighbor. The following limits apply to BGP configurations:

The default maximum number of peers that can be configured is 4000. The default can be changed usingthe bgp maximum neighbor command. The limit range is 1 to 15000. Any attempt to configureadditional peers beyond the maximum limit or set the maximum limit to a number that is less than thenumber of peers currently configured will fail.


Implementing BGPBGP Router Identifier

To prevent a peer from flooding BGP with advertisements, a limit is placed on the number of prefixesthat are accepted from a peer for each supported address family. The default limits can be overriddenthrough configuration of the maximum-prefix limit command for the peer for the appropriate addressfamily. The following default limits are used if the user does not configure the maximum number ofprefixes for the address family:

IPv4 Unicast: 1048576

IPv4 Multicast: 131072

IPv4 Labeled-unicast: 131072

VPNv4 Unicast: 2097152

IPv4 MDT: 131072

IPv4 Tunnel: 1048576

IPv6 Unicast: 524288

IPv6 Multicast: 131072

IPv6 Labeled-unicast: 131072

VPNv6 Unicast: 1048576

L2VPN EVPN: 2097152

A cease notification message is sent to the neighbor and the peering with the neighbor is terminatedwhen the number of prefixes received from the peer for a given address family exceeds the maximumlimit (either set by default or configured by the user) for that address family.

It is possible that the maximum number of prefixes for a neighbor for a given address family has beenconfigured after the peering with the neighbor has been established and a certain number of prefixeshave already been received from the neighbor for that address family. A cease notification message issent to the neighbor and peering with the neighbor is terminated immediately after the configuration ifthe configured maximum number of prefixes is fewer than the number of prefixes that have already beenreceived from the neighbor for the address family.

BGP Next Hop TrackingBGP receives notifications from the Routing Information Base (RIB) when next-hop information changes(event-driven notifications). BGP obtains next-hop information from the RIB to:

Determine whether a next hop is reachable.

Find the fully recursed IGP metric to the next hop (used in the best-path calculation).

Validate the received next hops.

Calculate the outgoing next hops.

Verify the reachability and connectedness of neighbors.

BGP is notified when any of the following events occurs:

Next hop becomes unreachable


Implementing BGPBGP Next Hop Tracking

Next hop becomes reachable

Fully recursed IGP metric to the next hop changes

First hop IP address or first hop interface change

Next hop becomes connected

Next hop becomes unconnected

Next hop becomes a local address

Next hop becomes a nonlocal address

Reachability and recursed metric events trigger a best-path recalculation.Note

Event notifications from the RIB are classified as critical and noncritical. Notifications for critical and noncriticalevents are sent in separate batches. However, a noncritical event is sent along with the critical events if thenoncritical event is pending and there is a request to read the critical events.

Critical events are related to the reachability (reachable and unreachable), connectivity (connected andunconnected), and locality (local and nonlocal) of the next hops. Notifications for these events are notdelayed.

Noncritical events include only the IGPmetric changes. These events are sent at an interval of 3 seconds.A metric change event is batched and sent 3 seconds after the last one was sent.

The next-hop trigger delay for critical and noncritical events can be configured to specify a minimum batchinginterval for critical and noncritical events using the nexthop trigger-delay command. The trigger delay isaddress family dependent.

The BGP next-hop tracking feature allows you to specify that BGP routes are resolved using only next hopswhose routes have the following characteristics:

To avoid the aggregate routes, the prefix length must be greater than a specified value.

The source protocol must be from a selected list, ensuring that BGP routes are not used to resolve nexthops that could lead to oscillation.

This route policy filtering is possible because RIB identifies the source protocol of route that resolved a nexthop as well as the mask length associated with the route. The nexthop route-policy command is used tospecify the route-policy.

For information on route policy filtering for next hops using the next-hop attach point, see the ImplementingRouting Policy Language on Cisco IOS XR Software module of Cisco IOS XR Routing ConfigurationGuide (this publication).

Next Hop as the IPv6 Address of Peering InterfaceBGP can carry IPv6 prefixes over an IPv4 session. The next hop for the IPv6 prefixes can be set through anexthop policy. In the event that the policy is not configured, the nexthops are set as the IPv6 address of thepeering interface (IPv6 neighbor interface or IPv6 update source interface, if any one of the interfaces isconfigured).



If the nexthop policy is not configured and neither the IPv6 neighbor interface nor the IPv6 update sourceinterface is configured, the next hop is the IPv4 mapped IPv6 address.

Scoped IPv4/VPNv4 Table WalkTo determine which address family to process, a next-hop notification is received by first dereferencing thegateway context associated with the next hop, then looking into the gateway context to determine whichaddress families are using the gateway context. The IPv4 unicast and VPNv4 unicast address families sharethe same gateway context, because they are registered with the IPv4 unicast table in the RIB. As a result, boththe global IPv4 unicast table and the VPNv4 table are processed when an IPv4 unicast next-hop notificationis received from the RIB. A mask is maintained in the next hop, indicating whether the next hop belongs toIPv4 unicast or VPNv4 unicast, or both. This scoped table walk localizes the processing in the appropriateaddress family table.

Reordered Address Family ProcessingThe Cisco IOS XR software walks address family tables based on the numeric value of the address family.When a next-hop notification batch is received, the order of address family processing is reordered to thefollowing order:

IPv4 tunnel

VPNv4 unicast

VPNv6 unicast

IPv4 labeled unicast

IPv4 unicast

IPv4 MDT

IPv4 multicast

IPv6 unicast

IPv6 multicast

IPv6 labeled unicast

New Thread for Next-Hop ProcessingThe critical-event thread in the spkr process handles only next-hop, Bidirectional Forwarding Detection (BFD),and fast-external-failover (FEF) notifications. This critical-event thread ensures that BGP convergence is notadversely impacted by other events that may take a significant amount of time.

show, clear, and debug CommandsThe show bgp nexthops command provides statistical information about next-hop notifications, the amountof time spent in processing those notifications, and details about each next hop registered with the RIB. Theclear bgp nexthop performance-statistics command ensures that the cumulative statistics associated withthe processing part of the next-hop show command can be cleared to help in monitoring. The clear bgpnexthop registration command performs an asynchronous registration of the next hop with the RIB. See the



BGP Commands on Cisco IOS XR Software module of Cisco IOS XR Routing Command Reference for theCisco CRS Routerfor information on the next-hop show and clear commands.

The debug bgp nexthop command displays information on next-hop processing. The out keyword providesdebug information only about BGP registration of next hops with RIB. The in keyword displays debuginformation about next-hop notifications received from RIB. The out keyword displays debug informationabout next-hop notifications sent to the RIB. See the BGP Debug Commands on Cisco IOS XR Softwaremodule of Cisco IOS XR Routing Debug Command Reference for the Cisco CRS-1 Router .

Autonomous System Number Formats in BGPAutonomous system numbers (ASNs) are globally unique identifiers used to identify autonomous systems(ASs) and enable ASs to exchange exterior routing information between neighboring ASs. A unique ASN isallocated to each AS for use in BGP routing. ASNs are encoded as 2-byte numbers and 4-byte numbers inBGP.

2-byte Autonomous System Number FormatThe 2-byte ASNs are represented in asplain notation. The 2-byte range is 1 to 65535.

4-byte Autonomous System Number FormatTo prepare for the eventual exhaustion of 2-byte Autonomous SystemNumbers (ASNs), BGP has the capabilityto support 4-byte ASNs. The 4-byte ASNs are represented both in asplain and asdot notations.

The byte range for 4-byte ASNs in asplain notation is 1-4294967295. The AS is represented as a 4-bytedecimal number. The 4-byte ASN asplain representation is defined in draft-ietf-idr-as-representation-01.txt.

For 4-byte ASNs in asdot format, the 4-byte range is 1.0 to 65535.65535 and the format is:

high-order-16-bit-value-in-decimal . low-order-16-bit-value-in-decimal

The BGP 4-byte ASN capability is used to propagate 4-byte-based AS path information across BGP speakersthat do not support 4-byte AS numbers. See draft-ietf-idr-as4bytes-12.txt for information on increasing thesize of an ASN from 2 bytes to 4 bytes. AS is represented as a 4-byte decimal number

as-format CommandThe as-format command configures the ASN notation to asdot. The default value, if the as-format commandis not configured, is asplain.

BGP ConfigurationBGP in Cisco IOS XR software follows a neighbor-based configuration model that requires that allconfigurations for a particular neighbor be grouped in one place under the neighbor configuration. Peer groupsare not supported for either sharing configuration between neighbors or for sharing update messages. Theconcept of peer group has been replaced by a set of configuration groups to be used as templates in BGPconfiguration and automatically generated update groups to share update messages between neighbors.


Implementing BGPAutonomous System Number Formats in BGP

Configuration ModesBGP configurations are grouped into modes. The following sections show how to enter some of the BGPconfiguration modes. From a mode, you can enter the ? command to display the commands available in thatmode.

Router Configuration Mode

The following example shows how to enter router configuration mode:

RP/0/RP0/CPU0:router# configurationRP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)#

Router Address Family Configuration Mode

The following example shows how to enter router address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 112RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 multicastRP/0/RP0/CPU0:router(config-bgp-af)#

Neighbor Configuration Mode

The following example shows how to enter neighbor configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.1RP/0/RP0/CPU0:router(config-bgp-nbr)#

Neighbor Address Family Configuration Mode

The following example shows how to enter neighbor address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 112RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.1RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-nbr-af)#

VRF Configuration Mode

The following example shows how to enter VPN routing and forwarding (VRF) configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_ARP/0/RP0/CPU0:router(config-bgp-vrf)#


Implementing BGPBGP Configuration

VRF Address Family Configuration Mode

The following example shows how to enter VRF address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 112RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_ARP/0/RP0/CPU0:router(config-bgp-vrf)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-vrf-af)#

VRF Neighbor Configuration Mode

The following example shows how to enter VRF neighbor configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_ARP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 11.0.1.2RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)#

VRF Neighbor Address Family Configuration Mode

The following example shows how to enter VRF neighbor address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 112RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_ARP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 11.0.1.2RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)#

VPNv4 Address Family Configuration Mode

The following example shows how to enter VPNv4 address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 152RP/0/RP0/CPU0:router(config-bgp)# address-family vpnv4 unicastRP/0/RP0/CPU0:router(config-bgp-af)#

VPNv6 Address Family Configuration Mode

The following example shows how to enter VPNv6 address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 150RP/0/RP0/CPU0:router(config-bgp)# address-family vpnv6 unicastRP/0/RP0/CPU0:router(config-bgp-af)#

L2VPN Address Family Configuration Mode

The following example shows how to enter L2VPN address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 100RP/0/RP0/CPU0:router(config-bgp)# address-family l2vpn vpls-vpws



RP/0/RP0/CPU0:router(config-bgp-af)#

Neighbor Submode Cisco IOS XR BGP uses a neighbor submode to make it possible to enter configurations without having toprefix every configuration with the neighbor keyword and the neighbor address:

Cisco IOS XR software has a submode available for neighbors in which it is not necessary for everycommand to have a neighbor x.x.x.x prefix:

In Cisco IOS XR software, the configuration is as follows:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.23.1.2RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 multicast

An address family configuration submode inside the neighbor configuration submode is available forentering address family-specific neighbor configurations. In Cisco IOS XR software, the configurationis as follows:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 2002::2RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2023RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv6 unicastRP/0/RP0/CPU0:router(config-bgp-nbr-af)# next-hop-selfRP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy one in

You must enter neighbor-specific IPv4, IPv6, VPNv4, or VPNv6 commands in neighbor address-familyconfiguration submode. In Cisco IOS XR software, the configuration is as follows:

RP/0/RP0/CPU0:router(config)# router bgp 109RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.40.24RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-nbr-af)# maximum-prefix 1000

Youmust enter neighbor-specific IPv4 and IPv6 commands in VRF neighbor address-family configurationsubmode. In Cisco IOS XR software, the configuration is as follows:

RP/0/RP0/CPU0:router(config)# router bgp 110RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_ARP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 11.0.1.2RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)# route-policy pass all in

Configuration TemplatesThe af-group, session-group, and neighbor-group configuration commands provide template support forthe neighbor configuration in Cisco IOS XR software.

The af-group command is used to group address family-specific neighbor commands within an IPv4, IPv6,VPNv4, or VPNv6 address family. Neighbors that have the same address family configuration are able to usethe address family group (af-group) name for their address family-specific configuration. A neighbor inheritsthe configuration from an address family group by way of the use command. If a neighbor is configured touse an address family group, the neighbor (by default) inherits the entire configuration from the address family



group. However, a neighbor does not inherit all of the configuration from the address family group if itemsare explicitly configured for the neighbor. The address family group configuration is entered under the BGProuter configuration mode. The following example shows how to enter address family group configurationmode :

RP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# af-group afmcast1 address-family ipv4 multicastRP/0/RP0/CPU0:router(config-bgp-afgrp)#

The session-group command allows you to create a session group from which neighbors can inherit addressfamily-independent configuration. A neighbor inherits the configuration from a session group by way of theuse command. If a neighbor is configured to use a session group, the neighbor (by default) inherits the entireconfiguration of the session group. A neighbor does not inherit all of the configuration from a session groupif a configuration is done directly on that neighbor. The following example shows how to enter session groupconfiguration mode:

RP/0/RP0/CPU0:router# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# session-group session1RP/0/RP0/CPU0:router(config-bgp-sngrp)#

The neighbor-group command helps you apply the same configuration to one or more neighbors. Neighborgroups can include session groups and address family groups and can comprise the complete configurationfor a neighbor. After a neighbor group is configured, a neighbor can inherit the configuration of the groupusing the use command. If a neighbor is configured to use a neighbor group, the neighbor inherits the entireBGP configuration of the neighbor group.

The following example shows how to enter neighbor group configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 123RP/0/RP0/CPU0:router(config-bgp)# neighbor-group nbrgroup1RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#

The following example shows how to enter neighbor group address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# neighbor-group nbrgroup1RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)#

However, a neighbor does not inherit all of the configuration from the neighbor group if items areexplicitly configured for the neighbor. In addition, some part of the configuration of the neighbor groupcould be hidden if a session group or address family group was also being used.

Configuration grouping has the following effects in Cisco IOS XR software:

Commands entered at the session group level define address family-independent commands (the samecommands as in the neighbor submode).

Commands entered at the address family group level define address family-dependent commands for aspecified address family (the same commands as in the neighbor-address family configuration submode).

Commands entered at the neighbor group level define address family-independent commands and addressfamily-dependent commands for each address family (the same as all available neighbor commands),and define the use command for the address family group and session group commands.



Template Inheritance RulesIn Cisco IOS XR software, BGP neighbors or groups inherit configuration from other configuration groups.

For address family-independent configurations:

Neighbors can inherit from session groups and neighbor groups.

Neighbor groups can inherit from session groups and other neighbor groups.

Session groups can inherit from other session groups.

If a neighbor uses a session group and a neighbor group, the configurations in the session group arepreferred over the global address family configurations in the neighbor group.

For address family-dependent configurations:

Address family groups can inherit from other address family groups.

Neighbor groups can inherit from address family groups and other neighbor groups.

Neighbors can inherit from address family groups and neighbor groups.

Configuration group inheritance rules are numbered in order of precedence as follows:

1 If the item is configured directly on the neighbor, that value is used. In the example that follows, theadvertisement interval is configured both on the neighbor group and neighbor configuration and theadvertisement interval being used is from the neighbor configuration:

RP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# neighbor-group AS_1RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 15RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor 10.1.1.1RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group AS_1RP/0/RP0/CPU0:router(config-bgp-nbr)# advertisement-interval 20

The following output from the show bgp neighbors command shows that the advertisement interval usedis 20 seconds:

RP/0/RP0/CPU0:router# show bgp neighbors 10.1.1.1

BGP neighbor is 10.1.1.1, remote AS 1, local AS 140, external linkRemote router ID 0.0.0.0BGP state = IdleLast read 00:00:00, hold time is 180, keepalive interval is 60 secondsReceived 0 messages, 0 notifications, 0 in queueSent 0 messages, 0 notifications, 0 in queueMinimum time between advertisement runs is 20 seconds

For Address Family: IPv4 UnicastBGP neighbor version 0Update group: 0.1eBGP neighbor with no inbound or outbound policy; defaults to 'drop'Route refresh request: received 0, sent 00 accepted prefixesPrefix advertised 0, suppressed 0, withdrawn 0, maximum limit 524288Threshold for warning message 75%

Connections established 0; dropped 0Last reset 00:00:14, due to BGP neighbor initializedExternal BGP neighbor not directly connected.



2 Otherwise, if an item is configured to be inherited from a session-group or neighbor-group and on theneighbor directly, then the configuration on the neighbor is used. If a neighbor is configured to be inheritedfrom session-group or af-group, but no directly configured value, then the value in the session-group oraf-group is used. In the example that follows, the advertisement interval is configured on a neighbor groupand a session group and the advertisement interval value being used is from the session group:

RP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# session-group AS_2RP/0/RP0/CPU0:router(config-bgp-sngrp)# advertisement-interval 15RP/0/RP0/CPU0:router(config-bgp-sngrp)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor-group AS_1RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 20RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.0.1RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1RP/0/RP0/CPU0:router(config-bgp-nbr)# use session-group AS_2RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group AS_1






3 Otherwise, if the neighbor uses a neighbor group and does not use a session group or address family group,the configuration value can be obtained from the neighbor group either directly or through inheritance. Inthe example that follows, the advertisement interval from the neighbor group is used because it is notconfigured directly on the neighbor and no session group is used:

RP/0/RP0/CPU0:router(config)# router bgp 150RP/0/RP0/CPU0:router(config-bgp)# session-group AS_2RP/0/RP0/CPU0:router(config-bgp-sngrp)# advertisement-interval 20RP/0/RP0/CPU0:router(config-bgp-sngrp)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor-group AS_1RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 15RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.1.1RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group AS_1



BGP neighbor is 192.168.2.2, remote AS 1, local AS 140, external link



Remote router ID 0.0.0.0BGP state = IdleLast read 00:00:00, hold time is 180, keepalive interval is 60 secondsReceived 0 messages, 0 notifications, 0 in queueSent 0 messages, 0 notifications, 0 in queueMinimum time between advertisement runs is 15 seconds

For Address Family: IPv4 UnicastBGP neighbor version 0Update group: 0.1eBGP neighbor with no outbound policy; defaults to 'drop'Route refresh request: received 0, sent 0Inbound path policy configuredPolicy for incoming advertisements is POLICY_10 accepted prefixesPrefix advertised 0, suppressed 0, withdrawn 0, maximum limit 524288Threshold for warning message 75%


To illustrate the same rule, the following example shows how to set the advertisement interval to 15 (fromthe session group) and 25 (from the neighbor group). The advertisement interval set in the session groupoverrides the one set in the neighbor group. The inbound policy is set to POLICY_1 from the neighborgroup.

RP/0/RP0/CPU0:routerconfig)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# session-group ADVRP/0/RP0/CPU0:router(config-bgp-sngrp)# advertisement-interval 15RP/0/RP0/CPU0:router(config-bgp-sngrp)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor-group ADV_2RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 25RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# route-policy POLICY_1 inRP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# exitRP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exitRP/0/RP0/CPU0:router(config-bgp)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.2.2RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1RP/0/RP0/CPU0:router(config-bgp-nbr)# use session-group ADVRP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group ADV_2








4 Otherwise, the default value is used. In the example that follows, neighbor 10.0.101.5 has the minimumtime between advertisement runs set to 30 seconds (default) because the neighbor is not configured to usethe neighbor configuration or the neighbor group configuration:

RP/0/RP0/CPU0:router(config)# router bgp 140RP/0/RP0/CPU0:router(config-bgp)# neighbor-group AS_1RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# remote-as 1RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor-group adv_15RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# remo

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