Configuring OSPF Graceful Restart

E Series routers support OSPF graceful restart extensions as defined in RFC 3623 (Graceful OSPF Restart). Graceful restart enables a router to continue forwarding OSPF traffic based on routing information it receives prior to an unplanned restart, while the E Series router switches from the primary SRP to the secondary SRP module.

Graceful restart helps to avoid interruptions in traffic forwarding and network-wide route changes when a route processor restarts or switches over to a redundant route processor.

To accomplish OSPF graceful restart, communication must take place between the router that is restarting and its OSPF neighbors. These neighboring routers must cooperate with (or help) the restarting router by keeping it in the forwarding path while it is restarting.

The restarting router sends a grace LSA (a link-local LSA) to inform its neighbors that it is restarting. After receiving this grace LSA, the neighbors act as if the router still exists in the network topology and continue forwarding traffic through the restarting router (for the specified grace period as defined in the grace LSA). If the restarting router does not become fully adjacent with the helper router before the grace period expires, the helper abandons the helper role and determines its adjacency with the restarting router to be down. Also, based on your configuration, the helper can abandon a restart if it detects a topology change before the restart is complete.

After the router restarts, the restarting router purges the grace LSA from the OSPF domain.

To configure the router as a graceful restart helper, use the graceful restart helper commands. These commands include graceful-restart helper and graceful-restart helper-abort-topology-change.

To configure the router for a restart scenario, use the graceful restart commands. These commands include graceful-restart, graceful-restart notify-time, and graceful-restart restart-time.

Note: We recommend that you always enable stateful SRP switchover on routers that you have configured with OSPF graceful restart—not doing so renders OSPF graceful restart configuration ineffective.

Note: Graceful restart mode and the OSPF graceful restart helper mode are supported for both OSPFv2 and OSPFv3 routers.

Note: For information about configuring hold timers for OSPF graceful restart in scaled environments, see the Configuring Hold Timers for Successful Graceful Restart in Scaled Scenarios section in the JunosE BGP and MPLS Configuration Guide.

graceful-restart

graceful-restart helper

graceful-restart helper-abort-topology-change

graceful-restart notify-time

graceful-restart restart-time