Configuring BGP GR

BGP GR can be configured to avoid traffic interruption due to protocol restart.

Context

BGP restart causes peer relationship reestablishment and traffic interruption. After GR is enabled, traffic interruption can be prevented in the event of BGP restart.

The following roles are involved in BGP GR:

GR restarter: is a device that is restarted by the administrator or in the case of a failure. The GR restarter must be a GR-capable device.
GR helper: is a neighbor of the GR restarter. The GR helper must also have the GR capability.

Procedure

Enable BGP GR.
A GR-capable device can establish GR sessions with a GR-capable neighbor. By controlling the session negotiation mechanism of BGP, the GR restarter and the GR helper can understand each other's GR capability. When detecting the restart of the GR restarter, the GR helper does not delete the routing and forwarding entries related to the GR restarter, but waits to re-establish a BGP connection with the GR restarter. After establishing a new BGP connection, the GR restarter and the GR helper update BGP routes.
1. Access the system view.
  system-view
2. Access the BGP view.
  bgp { as-number-plain | as-number-dot }
3. Enable BGP GR.
  graceful-restart
  
  By default, BGP GR is disabled.
4. (Optional) Enable the router to reset a BGP session in GR mode.
  graceful-restart peer-reset
  
  Currently, BGP does not support dynamic capability negotiation. Therefore, each time a new BGP capability is enabled on a router, the BGP speaker tears down existing sessions with its peer and renegotiates BGP capabilities. This process will interrupt ongoing services. To prevent the service interruptions, run the graceful-restart peer-reset command to enable the router to reset a BGP session in GR mode. Then, the router will not delete routing entries for existing sessions when a new BGP capability is enabled.
Configure parameters for a BGP GR session.
1. Access the system view.
  system-view
2. Access the BGP view.
  bgp { as-number-plain | as-number-dot }
3. Set the maximum period of time used for reestablishing a BGP session.
  graceful-restart timer restart time
  
  The restart period of the router is the maximum waiting period from the time when the GR helper discovers that the GR restarter restarts to the time when the BGP session is reestablished. By default, the restart period is 150 seconds.
  
  Changing the BGP restart period reestablishes BGP peer relationships.
4. Set the length of time the GR restarter and GR helper wait for End-of-RIB messages.
  graceful-restart timer wait-for-rib time
  
  By default, the time for waiting for End-Of-RIB messages is 600s.
  
  You can adjust BGP GR session parameter values as needed, but default values are recommended.