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Configuring Graceful Restart

OSPF supports two types of graceful restart: planned and unplanned. During a planned restart, the restarting router informs the neighbors before restarting. The neighbors act as if the router is still within the network topology, and continue forwarding traffic to the restarting router. A grace period is set to specify the time period for which the neighbors should consider the restarting router as part of the topology. During an unplanned restart, the router restarts without warning.

Note: On a broadcast link with a single neighbor, when the neighbor initiates an OSPFv3 graceful restart operation, the restart might be terminated at the point when the local router assumes the role of a helper. A change in the LSA is considered a topology change, which terminates the neighbor's restart operation.

Graceful restart is disabled by default. You can globally enable graceful restart for all routing protocols at the [edit routing-options] hierarchy level.

To configure graceful restart parameters specifically for OSPF, include the graceful-restart statement:




graceful-restart {
disable;
helper-disable;
notify-duration seconds;
restart-duration seconds;
}

For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.

To disable graceful restart, specify the disable statement. To configure a time period for complete reacquisition of OSPF neighbors, specify the restart-duration statement. To configure a time period for sending out purged grace LSAs over all interfaces, specify the notify-duration statement. Helper mode is enabled by default. To disable the graceful restart helper capability, specify the helper-disable statement.

The grace period interval for OSPF graceful restart is determined as equal to or smaller than the sum of the notify-duration time interval and the restart-duration time interval. The grace period is the number of seconds that the router's neighbors continue to advertise the router as fully adjacent, regardless of the connection state between the router and its neighbors.

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