BGP Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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BGP nonstop routing with stateful switchovers

Updated: February 28, 2026

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Overview

Describes BGP nonstop routing with stateful switchovers, including the configuration of NSR process-failures, operational flows of active and standby route processors during failures, feature behavior, and procedures to enable or disable BGP NSR.

A BGP nonstop routing is a network protocol feature that

  • enables all BGP peerings to maintain BGP states, and

  • ensures continuous packet forwarding without interruption visible to peer routers by maintaining protocol sessions and routing states across process restarts and switchovers.

Guidelines for BGP nonstop routing with stateful switchovers

  • Configure the nsr process-failures switchover command to maintain nonstop routing (NSR) during BGP or TCP process crashes.

  • Without this configuration, BGP neighbor sessions will flap, causing network instability.

  • NSR does not prevent session flapping during BGP or TCP process restarts; expect neighbor sessions to flap in such cases.

  • Additional measures beyond NSR are required to manage session flapping caused by process restarts.

  • This command is mandatory to ensure network stability during process failures.

How active and standby route processors work during switchovers and failures

Summary

This process explains how active and standby route processors, along with BGP and TCP processes, maintain continuous network operation during route processor switchovers or failures. The key components involved in the process are:

  • Active route processor: Manages routing and session handling under normal conditions.

  • Standby route processor: Synchronizes state with the active processor and takes over when needed.

  • BGP process: Maintains Border Gateway Protocol sessions and routing information.

  • TCP process: Maintains TCP connections supporting BGP sessions.

Workflow

The process involves the following stages:

  1. Switchover or failure detection: The system detects when the active route processor fails or switches over.
  2. State synchronization: Synchronization points ensure consistent internal state between active and standby BGP and TCP processes.
  3. Session migration: TCP connections and BGP sessions transparently migrate to the standby processor, which becomes active.
  4. Continuous forwarding: Packet forwarding continues uninterrupted without requiring peer routers to refresh protocol states or upgrade software.

Result

This process ensures uninterrupted packet forwarding and BGP session continuity during route processor switchovers or failures, maintaining network stability without manual intervention.

Capabilities and limitations of BGP nonstop routing

NSR maintains active BGP and TCP sessions during route processor switchovers, process crashes, and system upgrades by transparently failing over to the standby route processor without interrupting packet forwarding or causing session flaps. This ensures continuous network operation and enhances stability during critical events.

BGP nonstop routing capabilities

  • NSR-related alarms and notifications

  • Separate tracking of configured and operational NSR states

  • NSR statistics collection

  • NSR statistics display via show commands

  • XML schema support

  • Auditing mechanisms for active/standby state synchronization

  • CLI commands for NSR enablement and disablement

Events triggering NSR

  • Route processor switchovers

  • BGP or TCP process crashes or failures

  • Restart of l2vpn_mgr causing state flapping (no traffic loss)

  • In-Service System Upgrades (ISSUs) involving stateful switchover (SSO)

Enabled capabilities

  • Transparent migration of TCP connections and BGP sessions to standby route processor preserving protocol state without peer refresh

    NSR-related alarms and notifications

  • Separate tracking of configured and operational NSR states

  • Collection and display of NSR statistics via show commands

  • XML schema support for NSR data

  • Auditing mechanisms for state synchronization verification

  • Support for up to 5000 NSR sessions

  • No requirement for software upgrades or NSR support on peer routers

Limitations

  • NSR does not prevent session flapping if the BGP or TCP process restarts; expect neighbor sessions to flap in such cases.

  • When the l2vpn_mgr process restarts, the NSR client (te-control) may flap between Ready and Not Ready states, which is expected and causes no traffic loss.

Configuration requirements

  • Configure the nsr process-failures switchover command to maintain NSR during BGP or TCP process crashes or failures.

  • Without this command, BGP neighbor sessions will flap during process crashes.

  • NSR does not prevent session flapping during BGP or TCP process restarts; expect neighbor sessions to flap in such cases.

  • Additional measures beyond NSR may be required to manage session flapping caused by process restarts.

Additional operational notes

  • During route processor switchovers and In-Service System Upgrades (ISSUs), NSR is achieved by stateful switchover (SSO) of both TCP and BGP.

  • NSR does not require software upgrades on peer routers, nor do peers need to support NSR.

  • When a route processor switchover occurs due to a fault, TCP connections and BGP sessions migrate transparently to the standby RP, preserving protocol state without requiring peer refresh.

  • Events like soft reconfiguration and policy changes can alter BGP internal states; synchronization points called post-its keep active and standby BGP processes aligned.

Enable BGP NSR

Configure BGP NSR for BGP to enhance process resiliency.

NSR allows BGP sessions to remain up during process restarts. Enable NSR to improve network availability

Before you begin

Ensure you are in privileged EXEC mode on the router.

Save your current configuration.

Procedure

Enable NSR.

Example:

Router# router bgp 120
Routing(config-bgp)# nsr

The router enables BGP NSR as configured.

Disable BGP NSR

To remove non-stop routing for BGP or troubleshoot related issues, disable NSR for BGP.

NSR allows BGP sessions to remain up during process restarts. Disable NSR if troubleshooting or removing the feature.

Before you begin

Ensure you are in privileged EXEC mode on the router.

Save your current configuration.

Procedure

Disable NSR.

Example:

Router# router bgp 120
Routing(config-bgp)# no nsr

The router disables BGP NSR as configured.