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

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BGP fast fallover

Updated: February 28, 2026

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Overview

Details BGP Fast Fallover mechanisms for route protection, presents recommendations for stable and predictable operation, and provides steps to configure BGP fast-fallover.

BGP fast fallover is a routing feature that

  • quickly removes routes learned from directly connected iBGP or eBGP neighbors when an IP interface fails

  • accelerates the network convergence process by preventing the propagation of stale routes, and

  • eliminates the need to wait for the hold timer to expire when a directly attached interface fails.

When an interface attached to a directly connected BGP neighbor fails, routes learned from that neighbor typically persist until the hold timer expires. This lag can lead to slow network convergence and potential network instability. BGP Fast Fallover addresses this by ensuring routes are removed immediately. You can also use the nexthop trigger-delay command to quickly remove BGP routes of a failing neighbor, provided that the neighbor's BGP session endpoint is the same as the route's next hop.

Table 1. Feature History Table

Feature Name

Release Information

Feature Description

BGP Fast Fallover

 Release 25.4.1

Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*)

*This feature is now supported on:

  • 8011-32Y8L2H2FH

  • 8011-12G12X4Y-A

  • 8011-12G12X4Y-D

BGP Fast Fallover

 Release 25.1.1

Introduced in this release on: Fixed Systems (8700 [ASIC: K100])(select variants only*)

*This feature is supported on the Cisco 8011-4G24Y4H-I routers.

BGP Fast Fallover

 Release 24.4.1

Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100, K100])(select variants only); Modular Systems (8800 [LC ASIC: P100])(select variants only*)

*This feature is supported on:

  • 8212-48FH-M

  • 8711-32FH-M

  • 8712-MOD-M

  • 88-LC1-36EH

  • 88-LC1-12TH24FH-E

  • 88-LC1-52Y8H-EM

BGP Fast Fallover

Release 24.2.11

You can now terminate the external BGP sessions to an adjacent peer when the link to that peer goes down, without waiting for the hold timer to expire. With this feature you can enable fast fallover mechanism on a specific BGP neighbor even if bgp fast-external-fallover disable command is globally configured.

This feature enables quicker failure detection, and allows other recovery mechanisms to reroute the traffic quickly, thus resulting in faster convergence.

The feature introduces these changes:

CLI:

YANG Data Model:

Guidelines for BGP fast fallover

To ensure proper operation and network stability when using BGP fast fallover, follow these guidelines:

  • Apply fast fallover only to directly connected BGP neighbors. A directly connected neighbor is one that is either one hop away or has an IP address within the same subnet. Do not apply fast fallover to neighbors connected through loopback interfaces, even if they are one hop away.

  • Maintain established BGP sessions with neighbors that are not directly connected until a triggering event, such as hold timer expiration, causes the session to go down.

  • If an interface fails before fast fallover activates, manually clear the BGP neighbor session if necessary, as the BGP session does not automatically go down.

  • Allow the regular BGP session establishment process to proceed unchanged when an interface recovers from failure.

Follow these recommendations to maintain predictable BGP session behavior and ensure network stability when using the fast fallover feature.

Configure BGP fast fallover

This task describes how to enable and verify the BGP fast fallover feature for neighbors.

Before you begin

  • Verify you have appropriate access to the router’s configuration mode.

  • Confirm that you understand the network topology, especially which BGP neighbors are directly connected.

  • Ensure you have the necessary permissions to modify BGP neighbor configurations.

Procedure

1.

Enable fast fallover.

Example:

Router# configure
Router(config)# router bgp 120
Router(config-bgp)# neighbor 209.165.201.0
Router(config-bgp-nbr)# fast-fallover

  • By default, fast fallover is enabled for eBGP neighbors and disabled for iBGP neighbors.

  • If the bgp fast-external-fallover disable command is configured globally or in VRF mode, fast fallover is disabled for eBGP neighbors but can be overridden per neighbor using the fast-fallover command.

  • To stop the fast fallover setting from being inherited from a higher-level neighbor or session group, use the fast-fallover inheritance-disable command.
2.

Verify fast fallover configuration.

Example:

Use the show bgp neighbors ip-address or show run router bgp as-number neighbor ip-address command to check if fast fallover is enabled or inherited.

Router# show bgp neighbors 209.165.201.0
BGP neighbor is 209.165.201.0
...
fast-fallover
address-family ipv4 unicast
 use af-group ipv4_unicast_3_ibgp
...
Fast fallover is enabled
Neighbor is directly connected
Neighbor fast-fallover is configured
Neighbor is external and fast-external-fallover is not disabled
...
The presence of fast-fallover in the configuration output confirms that the feature is successfully configured for the neighbor.