Troubleshooting BGP: A Practical Guide to Understanding and Troubleshooting BGP

Description
Table of Contents

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.

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

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