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Troubleshooting BGP: A Practical Guide to Understanding and Troubleshooting BGP

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  • Description
  • Sample Content
  • Updates
  • Copyright 2017
  • Dimensions: 7-3/8" x 9-1/8"
  • Pages: 832
  • Edition: 1st
  • eBook (Watermarked)
  • ISBN-10: 0-13-443654-7
  • ISBN-13: 978-0-13-443654-8

The definitive guide to troubleshooting today’s complex BGP networks

This is today’s best single source for the techniques you need to troubleshoot BGP issues in modern Cisco IOS, IOS XR, and NxOS environments. BGP has expanded from being an Internet routing protocol and provides a scalable control plane for a variety of technologies, including MPLS VPNs and VXLAN. Bringing together content previously spread across multiple sources, Troubleshooting BGP describes BGP functions in today’s blended service provider and enterprise environments.

Two expert authors emphasize the BGP-related issues you’re most likely to encounter in real-world deployments, including problems that have caused massive network outages. They fully address convergence and scalability, as well as common concerns such as BGP slow peer, RT constraint filtering, and missing BGP routes. For each issue, key concepts are presented, along with basic configuration, detailed troubleshooting methods, and clear illustrations. Wherever appropriate, OS-specific behaviors are described and analyzed.

Troubleshooting BGP is an indispensable technical resource for all consultants, system/support engineers, and operations professionals working with BGP in even the largest, most complex environments.

·         Quickly review the BGP protocol, configuration, and commonly used features

·         Master generic troubleshooting methodologies that are relevant to BGP networks

·         Troubleshoot BGP peering issues, flapping peers, and dynamic BGP peering

·         Resolve issues related to BGP route installation, path selection, or route policies

·         Avoid and fix convergence problems

·         Address platform issues such as high CPU or memory usage

·         Scale BGP using route reflectors, diverse paths, and other advanced features

·         Solve problems with BGP edge architectures, multihoming, and load balancing

·         Secure BGP inter-domain routing with RPKI

·         Mitigate DDoS attacks with RTBH and BGP Flowspec

·         Understand common BGP problems with MPLS Layer 3 or Layer 2 VPN services

·         Troubleshoot IPv6 BGP for service providers, including 6PE and 6VPE

·         Overcome problems with VXLAN BGP EVPN data center deployments

·         Fully leverage BGP High Availability features, including GR, NSR, and BFD

·         Use new BGP enhancements for link-state distribution or tunnel setup

This book is part of the Networking Technology Series from Cisco Press, which offers networking professionals valuable information for constructing efficient networks, understanding new technologies, and building successful careers.

Table of Contents

Foreword xxii

Introduction xxiii

Part I BGP Fundamentals

Chapter 1 BGP Fundamentals 1

Border Gateway Protocol 1

    Autonomous System Numbers 2

    Path Attributes 3

    Loop Prevention 3

    Address Families 3

    BGP Sessions 4

Inter-Router Communication 5

BGP Messages 6

    OPEN 6

        Hold Time 6

        BGP Identifier 7


    UPDATE 7

    NOTIFICATION Message 8

BGP Neighbor States 8

    Idle 9

    Connect 9

    Active 10

    OpenSent 10

    OpenConfirm 10

    Established 10

Basic BGP Configuration 11

    IOS 11

    IOS XR 12

    NX-OS 13

    Verification of BGP Sessions 14

    Prefix Advertisement 17

    BGP Best-Path Calculation 20

Route Filtering and Manipulation 21


    IBGP Full Mesh Requirement 24

    Peering via Loopback Addresses 25


    EBGP and IBGP Topologies 28

    Next-Hop Manipulation 30

IBGP Scalability 31

    Route Reflectors 31

Loop Prevention in Route Reflectors 33

Out-of-Band Route Reflectors 33

    Confederations 34

BGP Communities 37

Route Summarization 38

    Aggregate-Address 39

    Flexible Route Suppression 40

        Selective Prefix Suppression 40

        Leaking Suppressed Routes 40

    Atomic Aggregate 40

    Route Aggregation with AS_SET 42

    Route Aggregation with Selective Advertisement of AS-SET 42

    Default Route Advertisement 42

    Default Route Advertisement per Neighbor 42

Remove Private AS 43

Allow AS 43

LocalAS 43

Summary 44

References 45

Part II Common BGP Troubleshooting

Chapter 2 Generic Troubleshooting Methodologies 47

Identifying the Problem 47

Understanding Variables 48

Reproducing the Problem 49

    Setting Up the Lab 49

    Configuring Lab Devices 52

    Triggering Events 56

Sniffer-Packet Capture 57

    SPAN on Cisco IOS 58

    SPAN on Cisco IOS XR 60

    SPAN on Cisco NX-OS 62

    Remote SPAN 63

Platform-Specific Packet Capture Tools 65

    Netdr Capture 66

    Embedded Packet Capture 68

    Ethanalyzer 70

Logging 74

Event Monitoring/Tracing 77

Summary 81

Reference 81

Chapter 3 Troubleshooting Peering Issues 83

BGP Peering Down Issues 83

    Verifying Configuration 84

    Verifying Reachability 87

        Find the Location and Direction of Packet Loss 88

        Verify Whether Packets Are Being Transmitted 89

        Use Access Control Lists to Verify Whether Packets Are Received 90

        Check ACLs and Firewalls in Path 91

        Verify TCP Sessions 94

        Simulate a BGP Session 95

    Demystifying BGP Notifications 96

    Decode BGP Messages 99

    Troubleshoot Blocked Process in IOS XR 103

        Verify BGP and BPM Process State 104

        Verify Blocked Processes 105

        Restarting a Process 106

    BGP Traces in IOS XR 106

    BGP Traces in NX-OS 108

    Debugs for BGP 110

    Troubleshooting IPv6 Peers 112

    Case Study–Single Session Versus Multisession 113

        Multisession Capability 114

        Single-Session Capability 115

BGP Peer Flapping Issues 115

    Bad BGP Update 115

    Hold Timer Expired 116

        Interface Issues 116

        Physical Connectivity 117

        Physical Interface 117

        Input Hold Queue 117

        TCP Receive Queue 119

    MTU Mismatch Issues 120

    High CPU Causing Control-Plane Flaps 125

    Control Plane Policing 127

        CoPP on NX-OS 129

        Local Packet Transport Services 134

Dynamic BGP Peering 138

    Dynamic BGP Peer Configuration 139

    Dynamic BGP Challenges 142

        Misconfigured MD5 Password 142

        Resource Issues in a Scaled Environment 142

        TCP Starvation 142

Summary 143

References 143

Chapter 4 Troubleshooting Route Advertisement and BGP Policies 145

Troubleshooting BGP Route Advertisement 145

    Local Route Advertisement Issues 145

    Route Aggregation Issues 147

    Route Redistribution Issues 150

    BGP Tables 152

    Receiving and Viewing Routes 154

Troubleshooting Missing BGP Routes 156

    Next-Hop Check Failures 157

    Bad Network Design 160

    Validity Check Failure 162

        AS-Path 162

        Originator-ID/Cluster-ID 165

    BGP Communities 167

        BGP Communities: No-Advertise 167

        BGP Communities: No-Export 169

        BGP Communities: Local-AS (No Export SubConfed) 170

        Mandatory EBGP Route Policy for IOS XR 172

    Filtering of Prefixes by Route Policy 173

Conditional Matching 174

    Access Control Lists (ACL) 174

    Prefix Matching 175

    Regular Expressions (Regex) 177

        UnderScore _ 179

        Caret ^ 180

        Dollar Sign $ 181

        Brackets [ ] 181

        Hyphen - 182

        Caret in Brackets [^] 182

        Parentheses ( ) and Pipe | 183

        Period . 183

        Plus Sign + 183

        Question Mark ? 184

        Asterisk * 184

        Looking Glass and Route Servers 185

    Conditionally Matching BGP Communities 185

Troubleshooting BGP Router Policies 185

    IOS and NX-OS Prefix-Lists 186

    IOS and NX-OS AS-Path ACLs 188

    Route-Map Processing 191

    IOS and NX-OS Route-Maps 192

    IOS XR Route-Policy Language 196

    Incomplete Configuration of Routing Policies 198

Conditional BGP Debugs 199

Summary 203

Further Reading 204

References in This Chapter 204

Chapter 5 Troubleshooting BGP Convergence 205

Understanding BGP Route Convergence 205

    BGP Update Groups 207

    BGP Update Generation 212

Troubleshooting Convergence Issues 216

    Faster Detection of Failures 218

        Jumbo MTU for Faster Convergence 219

        Slow Convergence due to Periodic BGP Scan 219

        Slow Convergence due to Default Route in RIB 222

        BGP Next-Hop Tracking 223

        Selective Next-Hop Tracking 225

        Slow Convergence due to Advertisement Interval 226

        Computing and Installing New Path 226

    Troubleshooting BGP Convergence on IOS XR 227

        Verifying Convergence During Initial Bring Up 227

        Verifying BGP Reconvergence in Steady State Network 228

    Troubleshooting BGP Convergence on NX-OS 234

BGP Slow Peer 237

    BGP Slow Peer Symptoms 238

        High CPU due to BGP Router Process 238

        Traffic Black Hole and Missing Prefixes in BGP table 238

    BGP Slow Peer Detection 239

        Verifying OutQ value 240

        Verifying SndWnd 240

        Verifying Cache Size and Pending Replication Messages 241

    Workaround 242

        Changing Outbound Policy 242

        Advertisement Interval 243

        BGP Slow Peer Feature 245

        Static Slow Peer 245

        Dynamic Slow Peer Detection 245

        Slow Peer Protection 246

    Slow Peer Show Commands 246

Troubleshooting BGP Route Flapping 246

Summary 250

Reference 250

Part III BGP Scalability Issues

Chapter 6 Troubleshooting Platform Issues Due to BGP 251

Troubleshooting High CPU Utilization due to BGP 251

    Troubleshooting High CPU due to BGP on Cisco IOS 252

        High CPU due to BGP Scanner Process 253

        High CPU due to BGP Router Process 255

        High CPU Utilization due to BGP I/O Process 256

    Troubleshooting High CPU due to BGP on IOS XR 258

        Troubleshooting High CPU due to BGP on NX-OS 262

        Capturing CPU History 265

        Troubleshooting Sporadic High CPU Condition 265

    Troubleshooting Memory Issues due to BGP 267

        TCAM Memory 269

        Troubleshooting Memory Issues on Cisco IOS Software 269

        Troubleshooting Memory Issues on IOS XR 274

        Troubleshooting Memory Issues on NX-OS 278

        Restarting Process 281

Summary 281

References 282

Chapter 7 Scaling BGP 283

The Impact of Growing Internet Routing Tables 283

Scaling Internet Table on Various Cisco Platforms 285

Scaling BGP Functions 288

    Tuning BGP Memory 290

        Prefixes 290

        Managing the Internet Routing Table 290

        Paths 292

        Attributes 293

    Tuning BGP CPU 295

        IOS Peer-Groups 295

        IOS XR BGP Templates 295

        NX-OS BGP Peer Templates 296

        BGP Peer Templates on Cisco IOS 297

        Soft Reconfiguration Inbound Versus Route Refresh 298

        Dynamic Refresh Update Group 302

        Enhanced Route Refresh Capability 305

    Outbound Route Filtering (ORF) 309

        Prefix-Based ORF 309

        Extended Community—Based ORF 309

        BGP ORF Format 310

        BGP ORF Configuration Example 312

    Maximum Prefixes 316

    BGP Max AS 318

    BGP Maximum Neighbors 322

Scaling BGP with Route Reflectors 322

    BGP Route Reflector Clusters 324

        Hierarchical Route Reflectors 331

        Partitioned Route Reflectors 332

        BGP Selective Route Download 339

        Virtual Route Reflectors 342

    BGP Diverse Path 346

        Shadow Route Reflectors 349

        Shadow Sessions 355

Route Servers 357

Summary 364

References 365

Chapter 8 Troubleshooting BGP Edge Architectures 367

BGP Multihoming and Multipath 367

    Resiliency in Service Providers 370

    EBGP and IBGP Multipath Configuration 370

    EIBGP Multipath 372

        R1 373

        R2 374

        R3 374

        R4 375

        R5 376

    AS-Path Relax 377

Understanding BGP Path Selection 377

    Routing Path Selection Longest Match 377

    BGP Best-Path Overview 379

        Weight 380

        Local Preference 380

        Locally Originated via Network or Aggregate Advertisement 380

        Accumulated Interior Gateway Protocol (AIGP) 381

        Shortest AS-Path 383

        Origin Type 383

        Multi-Exit Discriminator (MED) 384

        EBGP over IBGP 386

        Lowest IGP Metric 386

        Prefer the Oldest EBGP Path 387

        Router ID 387

        Minimum Cluster List Length 388

        Lowest Neighbor Address 388

Troubleshooting BGP Best Path 389

    Visualizing the Topology 390

        Phase I–Initial BGP Edge Route Processing 391

        Phase II–BGP Edge Evaluation of Multiple Paths 392

        Phase III–Final BGP Processing State 394

    Path Selection for the Routing Table 394

Common Issues with BGP Multihoming 395

    Transit Routing 395

    Problems with Race Conditions 397

    Peering on Cross-Link 402

        Expected Behavior 403

        Unexpected Behavior 406

        Secondary Verification Methods of a Routing Loop 409

        Design Enhancements 411

    Full Mesh with IBGP 412

    Problems with Redistributing BGP into an IGP 413

Summary 417

References 418

Part IV Securing BGP

Chapter 9 Securing BGP 419

The Need for Securing BGP 419

Securing BGP Sessions 420

    Explicitly Configured Peers 421

        IPv6 BGP Peering Using Link-Local Address 421

    BGP Session Authentication 424

        BGP Pass Through 426

    EBGP-Multihop 427

        BGP TTL Security 428

        Filtering 429

        Protecting BGP Traffic Using IPsec 431

Securing Interdomain Routing 431

    BGP Prefix Hijacking 432

    S-BGP 439

        IPsec 439

        Public Key Infrastructure 439

        Attestations 441

    soBGP 442

        Entity Certificate 442

        Authorization Certificate 443

        Policy Certificate 443

        BGP SECURITY Message 443

    BGP Origin AS Validation 443

        Route Origination Authorization (ROA) 445

        RPKI Prefix Validation Process 446

        Configuring and Verifying RPKI 449

        RPKI Best-Path Calculation 460

BGP Remote Triggered Black-Hole Filtering 463

BGP Flowspec 467

    Configuring BGP Flowspec 469

Summary 479

References 480

Part V Multiprotocol BGP

Chapter 10 MPLS Layer 3 VPN (L3VPN) 481


MPLS Layer 3 VPN (L3VPN) Overview 483

    Virtual Routing and Forwarding 483

    Route Distinguisher 485

    Route Target 485

    Multi-Protocol BGP (MP-BGP) 486

    Network Advertisement Between PE and CE Routers 487

MPLS Layer 3 VPN Configuration 487

    VRF Creation and Association 488

        IOS VRF Creation 488

        IOS XR VRF Creation 489

        NX-OS VRF Creation 490

    Verification of VRF Settings and Connectivity 492

        Viewing VRF Settings and Interface IP Addresses 492

        Viewing the VRF Routing Table 494

        VRF Connectivity Testing Tools 495

    MPLS Forwarding 495

    BGP Configuration for VPNv4 and PE-CE Prefixes 497

        IOS BGP Configuration for MPLS L3VPN 497

        IOS XR BGP Configuration for MPLS L3VPN 499

        NX-OS BGP Configuration for MPLS L3VPN 500

        Verification of BGP Sessions and Routes 502

Troubleshooting MPLS L3VPN 506

    Default Route Advertisement Between PE-CE Routers 508

    Problems with AS-PATH 509

    Suboptimal Routing with VPNv4 Route Reflectors 514

    Troubleshooting Problems with Route Targets 520

    MPLS L3VPN Services 524

    RT Constraints 534

    MPLS VPN Label Exchange 538

    MPLS Forwarding 541

Summary 542

References 542

Chapter 11 BGP for MPLS L2VPN Services 543

L2VPN Services 543

    Terminologies 545

    Virtual Private Wire Service 548

        Interworking 549

        Configuration and Verification 550

        VPWS BGP Signaling 558

        Configuration 560

    Virtual Private LAN Service 561

        Configuration 562

        Verification 564

        VPLS Autodiscovery Using BGP 569

        VPLS BGP Signaling 580

        Troubleshooting 586

Summary 588

References 589

Chapter 12 IPv6 BGP for Service Providers 591

IPv6 BGP Features and Concepts 591

    IPv6 BGP Next-Hop 591

    IPv6 Reachability over IPv4 Transport 596

    IPv4 Routes over IPv6 Next-Hop 601

    IPv6 BGP Policy Accounting 604

IPv6 Provider Edge Routers (6PE) over MPLS 607

    6PE Configuration 611

    6PE Verification and Troubleshooting 615

IPv6 VPN Provider Edge (6VPE) 620

    IPv6-Aware VRF 622

    6VPE Next-Hop 623

        Route Target 624

        6VPE Control Plane 624

    6VPE Data Plane 626

    6VPE Configuration 627

    6VPE Control-Plane Verification 629

    6VPE Data Plane Verification 633

Summary 639

References 639

Chapter 13 VxLAN BGP EVPN 641

Understanding VxLAN 641

    VxLAN Packet Structure 643

    VxLAN Gateway Types 645

VxLAN Overlay 645

    VxLAN Flood-and-Learn Mechanism 645

        Configuration and Verification 647

        Ingress Replication 652

Overview of VxLAN BGP EVPN 653

    Distributed Anycast Gateway 654

    ARP Suppression 655

    Integrated Route/Bridge (IRB) Modes 656

        Asymmetric IRB 657

        Symmetric IRB 658

    Multi-Protocol BGP 658

    Configuring and Verifying VxLAN BGP EVPN 661

Summary 690

References 691

Part VI High Availability

Chapter 14 BGP High Availability 693

BGP Graceful-Restart 693

BGP Nonstop Routing 700

Bidirectional Forwarding Detection 712

    Asynchronous Mode 713

    Asynchronous Mode with Echo Function 715

    Configuration and Verification 715

    Troubleshooting BFD Issues 724

        BFD Session Not Coming Up 724

        BFD Session Flapping 725

BGP Fast-External-Fallover 726

BGP Add-Path 726

BGP best-external 738

BGP FRR and Prefix-Independent Convergence 741

    BGP PIC Core 742

    BGP PIC Edge 745

        Scenario 1–IP PE-CE Link/Node Protection on CE Side 745

        Scenario 2–IP MPLS PE-CE Link/Node Protection for Primary/Backup 748

        BGP Recursion Host 752

Summary 753

References 753

Part VII BGP: Looking Forward

Chapter 15 Enhancements in BGP 755

Link-State Distribution Using BGP 755

    BGP-LS NLRI 759

    BGP-LS Path Attributes 762

    BGP-LS Configuration 762

        IGP Distribution 763

        BGP Link-State Session Initiation 763

BGP for Tunnel Setup 771

Provider Backbone Bridging: Ethernet VPN (PBB-EVPN) 773

    EVPN NLRI and Routes 776

    EVPN Extended Community 777

    EVPN Configuration and Verification 778

Summary 787

References 788

9781587144646   TOC   11/21/2016


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