Troubleshooting BGP: A Practical Guide to Understanding and Troubleshooting BGP (Networking Technology)

✍ Scribed by Vinit Jain, Brad Edgeworth

• Publisher: Cisco Press
• Year: 2016
• Tongue: English
• Leaves: 835
• Edition: 1
• Category: Library

✦ Synopsis

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

Cover
Title Page
Copyright Page
About the Authors
Acknowledgments
Contents
Foreword
Introduction
Part I: BGP Fundamentals
Chapter 1 BGP Fundamentals
Border Gateway Protocol
Autonomous System Numbers
Path Attributes
Loop Prevention
Address Families
BGP Sessions
Inter-Router Communication
BGP Messages
OPEN
Hold Time
BGP Identifier
KEEPALIVE
UPDATE
NOTIFICATION Message
BGP Neighbor States
Idle
Connect
Active
OpenSent
OpenConfirm
Established
Basic BGP Configuration
IOS
IOS XR
NX-OS
Verification of BGP Sessions
Prefix Advertisement
BGP Best-Path Calculation
Route Filtering and Manipulation
IBGP
IBGP Full Mesh Requirement
Peering via Loopback Addresses
EBGP
EBGP and IBGP Topologies
Next-Hop Manipulation
IBGP Scalability
Route Reflectors
Loop Prevention in Route Reflectors
Out-of-Band Route Reflectors
Confederations
BGP Communities
Route Summarization
Aggregate-Address
Flexible Route Suppression
Selective Prefix Suppression
Leaking Suppressed Routes
Atomic Aggregate
Route Aggregation with AS_SET
Route Aggregation with Selective Advertisement of AS-SET
Default Route Advertisement
Default Route Advertisement per Neighbor
Remove Private AS
Allow AS
LocalAS
Summary
References
Part II: Common BGP Troubleshooting
Chapter 2 Generic Troubleshooting Methodologies
Identifying the Problem
Understanding Variables
Reproducing the Problem
Setting Up the Lab
Configuring Lab Devices
Triggering Events
Sniffer-Packet Capture
SPAN on Cisco IOS
SPAN on Cisco IOS XR
SPAN on Cisco NX-OS
Remote SPAN
Platform-Specific Packet Capture Tools
Netdr Capture
Embedded Packet Capture
Ethanalyzer
Logging
Event Monitoring/Tracing
Summary
Reference
Chapter 3 Troubleshooting Peering Issues
BGP Peering Down Issues
Verifying Configuration
Verifying Reachability
Find the Location and Direction of Packet Loss
Verify Whether Packets Are Being Transmitted
Use Access Control Lists to Verify Whether Packets Are Received
Check ACLs and Firewalls in Path
Verify TCP Sessions
Simulate a BGP Session
Demystifying BGP Notifications
Decode BGP Messages
Troubleshoot Blocked Process in IOS XR
Verify BGP and BPM Process State
Verify Blocked Processes
Restarting a Process
BGP Traces in IOS XR
BGP Traces in NX-OS
Debugs for BGP
Troubleshooting IPv6 Peers
Case Study—Single Session Versus Multisession
Multisession Capability
Single-Session Capability
BGP Peer Flapping Issues
Bad BGP Update
Hold Timer Expired
Interface Issues
Physical Connectivity
Physical Interface
Input Hold Queue
TCP Receive Queue
MTU Mismatch Issues
High CPU Causing Control-Plane Flaps
Control Plane Policing
CoPP on NX-OS
Local Packet Transport Services
Dynamic BGP Peering
Dynamic BGP Peer Configuration
Dynamic BGP Challenges
Misconfigured MD5 Password
Resource Issues in a Scaled Environment
TCP Starvation
Summary
References
Chapter 4 Troubleshooting Route Advertisement and BGP Policies
Troubleshooting BGP Route Advertisement
Local Route Advertisement Issues
Route Aggregation Issues
Route Redistribution Issues
BGP Tables
Receiving and Viewing Routes
Troubleshooting Missing BGP Routes
Next-Hop Check Failures
Bad Network Design
Validity Check Failure
AS-Path
Originator-ID/Cluster-ID
BGP Communities
BGP Communities: No-Advertise
BGP Communities: No-Export
BGP Communities: Local-AS (No Export SubConfed)
Mandatory EBGP Route Policy for IOS XR
Filtering of Prefixes by Route Policy
Conditional Matching
Access Control Lists (ACL)
Prefix Matching
Regular Expressions (Regex)
UnderScore _
Caret ^
Dollar Sign $
Brackets [ ]
Hyphen -
Caret in Brackets [^]
Parentheses ( ) and Pipe |
Period
Plus Sign +
Question Mark ?
Asterisk *
Looking Glass and Route Servers
Conditionally Matching BGP Communities
Troubleshooting BGP Router Policies
IOS and NX-OS Prefix-Lists
IOS and NX-OS AS-Path ACLs
Route-Map Processing
IOS and NX-OS Route-Maps
IOS XR Route-Policy Language
Incomplete Configuration of Routing Policies
Conditional BGP Debugs
Summary
Further Reading
References in This Chapter
Chapter 5 Troubleshooting BGP Convergence
Understanding BGP Route Convergence
BGP Update Groups
BGP Update Generation
Troubleshooting Convergence Issues
Faster Detection of Failures
Jumbo MTU for Faster Convergence
Slow Convergence due to Periodic BGP Scan
Slow Convergence due to Default Route in RIB
BGP Next-Hop Tracking
Selective Next-Hop Tracking
Slow Convergence due to Advertisement Interval
Computing and Installing New Path
Troubleshooting BGP Convergence on IOS XR
Verifying Convergence During Initial Bring Up
Verifying BGP Reconvergence in Steady State Network
Troubleshooting BGP Convergence on NX-OS
BGP Slow Peer
BGP Slow Peer Symptoms
High CPU due to BGP Router Process
Traffic Black Hole and Missing Prefixes in BGP table
BGP Slow Peer Detection
Verifying OutQ value
Verifying SndWnd
Verifying Cache Size and Pending Replication Messages
Workaround
Changing Outbound Policy
Advertisement Interval
BGP Slow Peer Feature
Static Slow Peer
Dynamic Slow Peer Detection
Slow Peer Protection
Slow Peer Show Commands
Troubleshooting BGP Route Flapping
Summary
Reference
Part III: BGP Scalability Issues
Chapter 6 Troubleshooting Platform Issues Due to BGP
Troubleshooting High CPU Utilization due to BGP
Troubleshooting High CPU due to BGP on Cisco IOS
High CPU due to BGP Scanner Process
High CPU due to BGP Router Process
High CPU Utilization due to BGP I/O Process
Troubleshooting High CPU due to BGP on IOS XR
Troubleshooting High CPU due to BGP on NX-OS
Capturing CPU History
Troubleshooting Sporadic High CPU Condition
Troubleshooting Memory Issues due to BGP
TCAM Memory
Troubleshooting Memory Issues on Cisco IOS Software
Troubleshooting Memory Issues on IOS XR
Troubleshooting Memory Issues on NX-OS
Restarting Process
Summary
References
Chapter 7 Scaling BGP
The Impact of Growing Internet Routing Tables
Scaling Internet Table on Various Cisco Platforms
Scaling BGP Functions
Tuning BGP Memory
Prefixes
Managing the Internet Routing Table
Paths
Attributes
Tuning BGP CPU
IOS Peer-Groups
IOS XR BGP Templates
NX-OS BGP Peer Templates
BGP Peer Templates on Cisco IOS
Soft Reconfiguration Inbound Versus Route Refresh
Dynamic Refresh Update Group
Enhanced Route Refresh Capability
Outbound Route Filtering (ORF)
Prefix-Based ORF
Extended Community–Based ORF
BGP ORF Format
BGP ORF Configuration Example
Maximum Prefixes
BGP Max AS
BGP Maximum Neighbors
Scaling BGP with Route Reflectors
BGP Route Reflector Clusters
Hierarchical Route Reflectors
Partitioned Route Reflectors
BGP Selective Route Download
Virtual Route Reflectors
BGP Diverse Path
Shadow Route Reflectors
Shadow Sessions
Route Servers
Summary
References
Chapter 8 Troubleshooting BGP Edge Architectures
BGP Multihoming and Multipath
Resiliency in Service Providers
EBGP and IBGP Multipath Configuration
EIBGP Multipath
R1
R2
R3
R4
R5
AS-Path Relax
Understanding BGP Path Selection
Routing Path Selection Longest Match
BGP Best-Path Overview
Weight
Local Preference
Locally Originated via Network or Aggregate Advertisement
Accumulated Interior Gateway Protocol (AIGP)
Shortest AS-Path
Origin Type
Multi-Exit Discriminator (MED)
EBGP over IBGP
Lowest IGP Metric
Prefer the Oldest EBGP Path
Router ID
Minimum Cluster List Length
Lowest Neighbor Address
Troubleshooting BGP Best Path
Visualizing the Topology
Phase I—Initial BGP Edge Route Processing
Phase II—BGP Edge Evaluation of Multiple Paths
Phase III—Final BGP Processing State
Path Selection for the Routing Table
Common Issues with BGP Multihoming
Transit Routing
Problems with Race Conditions
Peering on Cross-Link
Expected Behavior
Unexpected Behavior
Secondary Verification Methods of a Routing Loop
Design Enhancements
Full Mesh with IBGP
Problems with Redistributing BGP into an IGP
Summary
References
Part IV: Securing BGP
Chapter 9 Securing BGP
The Need for Securing BGP
Securing BGP Sessions
Explicitly Configured Peers
IPv6 BGP Peering Using Link-Local Address
BGP Session Authentication
BGP Pass Through
EBGP-Multihop
BGP TTL Security
Filtering
Protecting BGP Traffic Using IPsec
Securing Interdomain Routing
BGP Prefix Hijacking
S-BGP
IPsec
Public Key Infrastructure
Attestations
soBGP
Entity Certificate
Authorization Certificate
Policy Certificate
BGP SECURITY Message
BGP Origin AS Validation
Route Origination Authorization (ROA)
RPKI Prefix Validation Process
Configuring and Verifying RPKI
RPKI Best-Path Calculation
BGP Remote Triggered Black-Hole Filtering
BGP Flowspec
Configuring BGP Flowspec
Summary
References
Part V: Multiprotocol BGP
Chapter 10 MPLS Layer 3 VPN (L3VPN)
MPLS VPNs
MPLS Layer 3 VPN (L3VPN) Overview
Virtual Routing and Forwarding
Route Distinguisher
Route Target
Multi-Protocol BGP (MP-BGP)
Network Advertisement Between PE and CE Routers
MPLS Layer 3 VPN Configuration
VRF Creation and Association
IOS VRF Creation
IOS XR VRF Creation
NX-OS VRF Creation
Verification of VRF Settings and Connectivity
Viewing VRF Settings and Interface IP Addresses
Viewing the VRF Routing Table
VRF Connectivity Testing Tools
MPLS Forwarding
BGP Configuration for VPNv4 and PE-CE Prefixes
IOS BGP Configuration for MPLS L3VPN
IOS XR BGP Configuration for MPLS L3VPN
NX-OS BGP Configuration for MPLS L3VPN
Verification of BGP Sessions and Routes
Troubleshooting MPLS L3VPN
Default Route Advertisement Between PE-CE Routers
Problems with AS-PATH
Suboptimal Routing with VPNv4 Route Reflectors
Troubleshooting Problems with Route Targets
MPLS L3VPN Services
RT Constraints
MPLS VPN Label Exchange
MPLS Forwarding
Summary
References
Chapter 11 BGP for MPLS L2VPN Services
L2VPN Services
Terminologies
Virtual Private Wire Service
Interworking
Configuration and Verification
VPWS BGP Signaling
Configuration
Virtual Private LAN Service
Configuration
Verification
VPLS Autodiscovery Using BGP
VPLS BGP Signaling
Troubleshooting
Summary
References
Chapter 12 IPv6 BGP for Service Providers
IPv6 BGP Features and Concepts
IPv6 BGP Next-Hop
IPv6 Reachability over IPv4 Transport
IPv4 Routes over IPv6 Next-Hop
IPv6 BGP Policy Accounting
IPv6 Provider Edge Routers (6PE) over MPLS
6PE Configuration
6PE Verification and Troubleshooting
IPv6 VPN Provider Edge (6VPE)
IPv6-Aware VRF
6VPE Next-Hop
Route Target
6VPE Control Plane
6VPE Data Plane
6VPE Configuration
6VPE Control-Plane Verification
6VPE Data Plane Verification
Summary
References
Chapter 13 VxLAN BGP EVPN
Understanding VxLAN
VxLAN Packet Structure
VxLAN Gateway Types
VxLAN Overlay
VxLAN Flood-and-Learn Mechanism
Configuration and Verification
Ingress Replication
Overview of VxLAN BGP EVPN
Distributed Anycast Gateway
ARP Suppression
Integrated Route/Bridge (IRB) Modes
Asymmetric IRB
Symmetric IRB
Multi-Protocol BGP
Configuring and Verifying VxLAN BGP EVPN
Summary
References
Part VI: High Availability
Chapter 14 BGP High Availability
BGP Graceful-Restart
BGP Nonstop Routing
Bidirectional Forwarding Detection
Asynchronous Mode
Asynchronous Mode with Echo Function
Configuration and Verification
Troubleshooting BFD Issues
BFD Session Not Coming Up
BFD Session Flapping
BGP Fast-External-Fallover
BGP Add-Path
BGP best-external
BGP FRR and Prefix-Independent Convergence
BGP PIC Core
BGP PIC Edge
Scenario 1—IP PE-CE Link/Node Protection on CE Side
Scenario 2—IP MPLS PE-CE Link/Node Protection for Primary/ Backup
BGP Recursion Host
Summary
References
Part VII: BGP: Looking Forward
Chapter 15 Enhancements in BGP
Link-State Distribution Using BGP
BGP-LS NLRI
BGP-LS Path Attributes
BGP-LS Configuration
IGP Distribution
BGP Link-State Session Initiation
BGP for Tunnel Setup
Provider Backbone Bridging: Ethernet VPN (PBB-EVPN)
EVPN NLRI and Routes
EVPN Extended Community
EVPN Configuration and Verification
Summary
References
Index
A
B
C
D
E
F
G
H
I
J-L
M
N
O
P
Q
R
S
T
U
V
W-Z