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Troubleshooting BGP: A Practical Guide to Understanding and Troubleshooting BGP

Book Description

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

  1. About This E-Book
  2. Title Page
  3. Copyright Page
  4. About the Authors
  5. About the Technical Reviewers
  6. Dedications
  7. Acknowledgments
  8. Contents at a Glance
  9. Contents
  10. Icons Used in This Book
  11. Command Syntax Conventions
  12. Foreword
  13. Introduction
    1. Who Should Read This Book?
    2. How This Book Is Organized
    3. Learning in a Lab Environment
    4. Additional Reading
  14. Part I: BGP Fundamentals
    1. Chapter 1. BGP Fundamentals
      1. Border Gateway Protocol
        1. Autonomous System Numbers
        2. Path Attributes
        3. Loop Prevention
        4. Address Families
        5. BGP Sessions
      2. Inter-Router Communication
      3. BGP Messages
        1. OPEN
        2. KEEPALIVE
        3. UPDATE
        4. NOTIFICATION Message
      4. BGP Neighbor States
        1. Idle
        2. Connect
        3. Active
        4. OpenSent
        5. OpenConfirm
        6. Established
      5. Basic BGP Configuration
        1. IOS
        2. IOS XR
        3. NX-OS
        4. Verification of BGP Sessions
        5. Prefix Advertisement
        6. BGP Best-Path Calculation
      6. Route Filtering and Manipulation
      7. IBGP
        1. IBGP Full Mesh Requirement
        2. Peering via Loopback Addresses
      8. EBGP
        1. EBGP and IBGP Topologies
        2. Next-Hop Manipulation
      9. IBGP Scalability
        1. Route Reflectors
      10. Loop Prevention in Route Reflectors
      11. Out-of-Band Route Reflectors
        1. Confederations
      12. BGP Communities
      13. Route Summarization
        1. Aggregate-Address
        2. Flexible Route Suppression
        3. Atomic Aggregate
        4. Route Aggregation with AS_SET
        5. Route Aggregation with Selective Advertisement of AS-SET
        6. Default Route Advertisement
        7. Default Route Advertisement per Neighbor
      14. Remove Private AS
      15. Allow AS
      16. LocalAS
      17. Summary
      18. References
  15. Part II: Common BGP Troubleshooting
    1. Chapter 2. Generic Troubleshooting Methodologies
      1. Identifying the Problem
      2. Understanding Variables
      3. Reproducing the Problem
        1. Setting Up the Lab
        2. Configuring Lab Devices
        3. Triggering Events
      4. Sniffer-Packet Capture
        1. SPAN on Cisco IOS
        2. SPAN on Cisco IOS XR
        3. SPAN on Cisco NX-OS
        4. Remote SPAN
      5. Platform-Specific Packet Capture Tools
        1. Netdr Capture
        2. Embedded Packet Capture
        3. Ethanalyzer
      6. Logging
      7. Event Monitoring/Tracing
      8. Summary
      9. Reference
    2. Chapter 3. Troubleshooting Peering Issues
      1. BGP Peering Down Issues
        1. Verifying Configuration
        2. Verifying Reachability
        3. Demystifying BGP Notifications
        4. Decode BGP Messages
        5. Troubleshoot Blocked Process in IOS XR
        6. BGP Traces in IOS XR
        7. BGP Traces in NX-OS
        8. Debugs for BGP
        9. Troubleshooting IPv6 Peers
        10. Case Study—Single Session Versus Multisession
      2. BGP Peer Flapping Issues
        1. Bad BGP Update
        2. Hold Timer Expired
        3. MTU Mismatch Issues
        4. High CPU Causing Control-Plane Flaps
        5. Control Plane Policing
      3. Dynamic BGP Peering
        1. Dynamic BGP Peer Configuration
        2. Dynamic BGP Challenges
      4. Summary
      5. References
    3. Chapter 4. Troubleshooting Route Advertisement and BGP Policies
      1. Troubleshooting BGP Route Advertisement
        1. Local Route Advertisement Issues
        2. Route Aggregation Issues
        3. Route Redistribution Issues
        4. BGP Tables
        5. Receiving and Viewing Routes
      2. Troubleshooting Missing BGP Routes
        1. Next-Hop Check Failures
        2. Bad Network Design
        3. Validity Check Failure
        4. BGP Communities
        5. Filtering of Prefixes by Route Policy
      3. Conditional Matching
        1. Access Control Lists (ACL)
        2. Prefix Matching
        3. Regular Expressions (Regex)
        4. Conditionally Matching BGP Communities
      4. Troubleshooting BGP Router Policies
        1. IOS and NX-OS Prefix-Lists
        2. IOS and NX-OS AS-Path ACLs
        3. Route-Map Processing
        4. IOS and NX-OS Route-Maps
        5. IOS XR Route-Policy Language
        6. Incomplete Configuration of Routing Policies
      5. Conditional BGP Debugs
      6. Summary
      7. Further Reading
      8. References in This Chapter
    4. Chapter 5. Troubleshooting BGP Convergence
      1. Understanding BGP Route Convergence
        1. BGP Update Groups
        2. BGP Update Generation
      2. Troubleshooting Convergence Issues
        1. Faster Detection of Failures
        2. Troubleshooting BGP Convergence on IOS XR
        3. Troubleshooting BGP Convergence on NX-OS
      3. BGP Slow Peer
        1. BGP Slow Peer Symptoms
        2. BGP Slow Peer Detection
        3. Workaround
        4. Slow Peer Show Commands
      4. Troubleshooting BGP Route Flapping
      5. Summary
      6. Reference
  16. Part III: BGP Scalability Issues
    1. Chapter 6. Troubleshooting Platform Issues Due to BGP
      1. Troubleshooting High CPU Utilization due to BGP
        1. Troubleshooting High CPU due to BGP on Cisco IOS
        2. Troubleshooting High CPU due to BGP on IOS XR
        3. Troubleshooting Memory Issues due to BGP
      2. Summary
      3. References
    2. Chapter 7. Scaling BGP
      1. The Impact of Growing Internet Routing Tables
      2. Scaling Internet Table on Various Cisco Platforms
      3. Scaling BGP Functions
        1. Tuning BGP Memory
        2. Tuning BGP CPU
        3. Outbound Route Filtering (ORF)
        4. Maximum Prefixes
        5. BGP Max AS
        6. BGP Maximum Neighbors
      4. Scaling BGP with Route Reflectors
        1. BGP Route Reflector Clusters
        2. BGP Diverse Path
      5. Route Servers
      6. Summary
      7. References
    3. Chapter 8. Troubleshooting BGP Edge Architectures
      1. BGP Multihoming and Multipath
        1. Resiliency in Service Providers
        2. EBGP and IBGP Multipath Configuration
        3. EIBGP Multipath
        4. AS-Path Relax
      2. Understanding BGP Path Selection
        1. Routing Path Selection Longest Match
        2. BGP Best-Path Overview
      3. Troubleshooting BGP Best Path
        1. Visualizing the Topology
        2. Path Selection for the Routing Table
      4. Common Issues with BGP Multihoming
        1. Transit Routing
        2. Problems with Race Conditions
        3. Peering on Cross-Link
        4. Full Mesh with IBGP
        5. Problems with Redistributing BGP into an IGP
      5. Summary
      6. References
  17. Part IV: Securing BGP
    1. Chapter 9. Securing BGP
      1. The Need for Securing BGP
      2. Securing BGP Sessions
        1. Explicitly Configured Peers
        2. BGP Session Authentication
        3. EBGP-Multihop
        4. Filtering
      3. Securing Interdomain Routing
        1. S-BGP
        2. soBGP
        3. BGP Origin AS Validation
      4. BGP Remote Triggered Black-Hole Filtering
      5. BGP Flowspec
        1. Configuring BGP Flowspec
      6. Summary
      7. References
  18. Part V: Multiprotocol BGP
    1. Chapter 10. MPLS Layer 3 VPN (L3VPN)
      1. MPLS VPNs
      2. MPLS Layer 3 VPN (L3VPN) Overview
        1. Virtual Routing and Forwarding
        2. Route Distinguisher
        3. Route Target
        4. Multi-Protocol BGP (MP-BGP)
        5. Network Advertisement Between PE and CE Routers
      3. MPLS Layer 3 VPN Configuration
        1. VRF Creation and Association
        2. Verification of VRF Settings and Connectivity
        3. MPLS Forwarding
        4. BGP Configuration for VPNv4 and PE-CE Prefixes
      4. Troubleshooting MPLS L3VPN
        1. Default Route Advertisement Between PE-CE Routers
        2. Problems with AS-PATH
        3. Suboptimal Routing with VPNv4 Route Reflectors
        4. Troubleshooting Problems with Route Targets
        5. MPLS L3VPN Services
        6. RT Constraints
        7. MPLS VPN Label Exchange
        8. MPLS Forwarding
      5. Summary
      6. References
    2. Chapter 11. BGP for MPLS L2VPN Services
      1. L2VPN Services
        1. Terminologies
        2. Virtual Private Wire Service
        3. Virtual Private LAN Service
      2. Summary
      3. References
    3. Chapter 12. IPv6 BGP for Service Providers
      1. IPv6 BGP Features and Concepts
        1. IPv6 BGP Next-Hop
        2. IPv6 Reachability over IPv4 Transport
        3. IPv4 Routes over IPv6 Next-Hop
        4. IPv6 BGP Policy Accounting
      2. IPv6 Provider Edge Routers (6PE) over MPLS
        1. 6PE Configuration
        2. 6PE Verification and Troubleshooting
      3. IPv6 VPN Provider Edge (6VPE)
        1. IPv6-Aware VRF
        2. 6VPE Next-Hop
        3. 6VPE Data Plane
        4. 6VPE Configuration
        5. 6VPE Control-Plane Verification
        6. 6VPE Data Plane Verification
      4. Summary
      5. References
    4. Chapter 13. VxLAN BGP EVPN
      1. Understanding VxLAN
        1. VxLAN Packet Structure
        2. VxLAN Gateway Types
      2. VxLAN Overlay
        1. VxLAN Flood-and-Learn Mechanism
      3. Overview of VxLAN BGP EVPN
        1. Distributed Anycast Gateway
        2. ARP Suppression
        3. Integrated Route/Bridge (IRB) Modes
        4. Multi-Protocol BGP
        5. Configuring and Verifying VxLAN BGP EVPN
      4. Summary
      5. References
  19. Part VI: High Availability
    1. Chapter 14. BGP High Availability
      1. BGP Graceful-Restart
      2. BGP Nonstop Routing
      3. Bidirectional Forwarding Detection
        1. Asynchronous Mode
        2. Asynchronous Mode with Echo Function
        3. Configuration and Verification
        4. Troubleshooting BFD Issues
      4. BGP Fast-External-Fallover
      5. BGP Add-Path
      6. BGP best-external
      7. BGP FRR and Prefix-Independent Convergence
        1. BGP PIC Core
        2. BGP PIC Edge
      8. Summary
      9. References
  20. Part VII: BGP: Looking Forward
    1. Chapter 15. Enhancements in BGP
      1. Link-State Distribution Using BGP
        1. BGP-LS NLRI
        2. BGP-LS Path Attributes
        3. BGP-LS Configuration
      2. BGP for Tunnel Setup
      3. Provider Backbone Bridging: Ethernet VPN (PBB-EVPN)
        1. EVPN NLRI and Routes
        2. EVPN Extended Community
        3. EVPN Configuration and Verification
      4. Summary
      5. References
  21. Index
  22. Code Snippets