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.

Vinit Jain, CCIE No. 22854 (R&S, SP, Security & DC), is a High Touch Technical Support (HTTS) engineer with Cisco providing support to premium customers of Cisco on complex routing technologies. Before joining Cisco, Vinit worked as a CCIE trainer and a network consultant. In addition to his expertise in networks, he has experience with software development, with which he began his career.

Vinit holds certifications for multiple vendors, such as Cisco, Microsoft, Sun Microsystems, VMware, and Oracle, and also is a Certified Ethical Hacker. Vinit is a speaker at Cisco Live and various other forums, including NANOG. Vinit pursued his graduation from Delhi University in Mathematics and earned his Masters in Information Technology from Kuvempu University in India. Vinit is married and is presently based out of RTP, North Carolina. Vinit can be found on Twitter @vinugenie.

Brad Edgeworth, CCIE No. 31574 (R&S & SP), has been with Cisco working as a systems engineer and a technical leader. Brad is a distinguished speaker at Cisco Live, where he has presented on multiple topics. Before joining Cisco, Brad worked as a network architect and consulted for various Fortune 500 companies. Brad's other certifications include Cisco Certified Design Professional (CCDP) and Microsoft Certified Systems Engineer (MCSE). Brad has been working in the IT field with an emphasis on enterprise and service provider environments from an architectural and operational perspective. Brad holds a Bachelor of Arts degree in Computer Systems Management from St. Edward's University in Austin, Texas. Brad can be found on Twitter @BradEdgeworth.

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

KEEPALIVE 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 22

IBGP Full Mesh Requirement 24

Peering via Loopback Addresses 25

EBGP 26

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

I…