OSPFv2 Graceful Restart
The graceful restart (GR) feature
provides a routing device with the capability to inform its neighbors when it is performing
a restart.
Neighboring devices, known as GR helpers, are
informed by protocol extensions that the device is undergoing a restart and assist in
the restart. For the duration of the graceful restart, the restarting device and its
neighbors continue forwarding packets, ensuring that there is no disruption to network
performance or topology. Disruptions in forwarding are minimized and route flapping
diminished. When the restart is complete, the device can quickly resume full operation
because of the assistance of the GR helpers. The adjacent devices then return to normal
operation.
There are two types of OSPFv2 graceful restart:
-
Planned restart: The restarting routing device informs its neighbors before performing the restart. The GR helpers act as if the routing device is still within the network topology, continuing to forward traffic to the restarting routing device. A defined interval, known as a “grace period” is set to specify when the neighbors should consider the restart complete and the restarting routing device as part of the network topology again.
- Unplanned restart: The routing device restarts without warning due to a
software fault.
Note
- For a graceful restart on a routing device to be successful, the OSPFv2
neighbors must have GR-helper mode enabled. GR-helper mode is enabled by
default.
- Process restart takes precedence over GR or non-stop routing (NSR).
