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 via 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 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 is able to quickly resume full operation due to 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
In order 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.

The table below shows GR support for OSPFv2.

Table 41 Graceful restart support for OSPFv2
GR restarting router GR helper NSR (no neighbor support needed)
Yes Yes Yes
Parent topic: OSPFv2