BGP graceful restart (GR) is high availability solutions that minimize the impact of device failures on user services.
BGP GR ensures that the forwarding plane continues to guide data forwarding during a device restart or active/standby switchover. The operations on the control plane, such as reestablishing peer relationships and performing route calculation, do not affect the forwarding plane. This mechanism prevents service interruptions caused by route flapping and improves network reliability.
GR concepts are as follows:
GR restarter
The device that is restarted by the administrator or triggered by failures to perform GR.
GR helper
The neighbor that helps the GR restarter to perform GR.
GR time
The time during which the GR helper retains forwarding information after detecting the restart or active/standby switchover of the GR restarter.
Using the BGP capability negotiation mechanism, the GR restarter and helper know each other's GR capability and establish a GR session.
When detecting the restart or active/standby switchover of the GR restarter, the GR helper waits to reestablish a BGP connection with the GR restarter. It does not delete the routing information and forwarding entries of the GR restarter or notify other neighbors of the restart or switchover.
The GR restarter reestablishes neighbor relationships with all GR helpers before the GR time expires.