The GR feature provides a routing device with the capability to inform its neighbors when it is performing a restart.
Note
Process restart takes precedence over graceful restart.When a BGP session is established, GR capability for BGP is negotiated by neighbors through the BGP OPEN message. If the neighbor also advertises support for GR, GR is activated for that neighbor session. If neither peer exchanges the GR capability, the session is not GR-capable. If the BGP session is lost, the BGP peer router, known as a GR helper, marks all routes associated with the device as “stale” but continues to forward packets to these routes for a set period of time. The restarting device also continues to forward packets for the duration of the graceful restart. When the graceful restart is complete, routes are obtained from the helper so that the device is able to quickly resume full operation.
When the GR feature is configured on a device, both helper router and restarting router functionalities are supported. It is not possible to disable helper functionality explicitly.
GR is disabled by default and can be enabled for both IPv4 and IPv6 address families. When the GR timer expires, the BGP RASlog message is triggered.
Note
BGP4 GR can be configured for a global routing instance or for a specified VRF instance. GR can also be configured on each individual BGP neighbor.