28.3.3 Restart function

The restart function of OSPFv3 operates at the following timing.

When switching of the master switch occurs in the stack configuration.
When the unicast routing program restarts.

<Structure of this section>

(1) GraceLSA

The Switch advertises GraceLSA of Type11 to notify the beginning and end of a graceful restart. This LSA format is draft-ietf-ospf-ospfv3-graceful-restart compliant.

(2) Graceful restart procedure

The following figures and tables show the graceful restart procedure for OSPFv3.

Figure 28-5: OSPFv3 graceful restart procedure

Table 28-4 OSPFv3 graceful restart procedure
No.	Item	Trigger	Process Description
1	Starting graceful restart	When the master switch is switched during stack configuration.	Starts a graceful restart. As with normal connectivity, interfaces exchange OSPFv3 packets.
1	Starting graceful restart	When the unicast routing program restarts.
2	Route calculation	When reconnection is completed for all OSPFv3 interfaces in the domain, and all LSA are learned from neighboring routers.	Route calculations are performed for each domain, and the routing table is updated. If there are multiple domains, the route calculation is performed from time to time from the domain where the connection is terminated. When route computation is completed for all domains, OSPFv3 route learning is completed.
2	Route calculation	A graceful restart has failed on a single interface.	Route calculations are based on the connection status of each interface in the same domain at that time.
3	Start of advertising	When route learning for OSPFv3 is complete and route learning for other routing protocols is complete.	Advertisement of external AS routes starts. After the advertisement is completed, OSPFv3 returns to normal operation.
3	Start of advertising	A graceful restart of OSPFv3 failed.

(3) When graceful restart fails

The graceful restart of OSPFv3 fails in the following cases:

When LSA learning cannot be completed even after the restart time (specified in graceful-restart restart-time of OSPFv3 configuration command) elapses after the graceful restart has been notified to the helper router
When the reconnected interface goes down
If LSA is changed on OSPFv3
When another router on OSPFv3 domain performs a graceful restart
When route learning for all protocols is not completed even after the route retention period (specified by the configuration command routing options graceful-restart time-limit) elapses after graceful restart starts
When the restart function is deleted by changing the configuration command graceful-restart mode

(4) Notes

Even if graceful restart is started as a restart router, if some helper routers do not start helper operation or stop in the middle, graceful restart is stopped on all interfaces in the same domain.
Set the restart time of OSPFv3 to exceed the switching time of the master switch + LSA learning time. This is because in order for OSPFv3 to learn LSA, the master switch must be switched and Up/Down of IP interfaces must be visible. After a graceful restart starts, if LSA has not been learned after the restart period has elapsed, OSPFv3 graceful restart fails.
Set the retention time for routing entries when the Switch restarts gracefully longer than OSPFv3 restart time. If the routing entry retention time is shorter than OSPFv3 restart time, routing entries prior to graceful restart might be deleted prior to route learning.
If the internal peer of BGP4+ is using graceful restart, set the restart time of the internal peer longer than the restart time of OSPFv3. If the internal peer restart time is shorter, the internal peer might fail to gracefully restart because the internal peer cannot be connected before OSPFv3 has completed route learning.