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 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 EB.