Understanding Restart Signaling-Based Helper Mode Support for OSPF Graceful Restart
Starting with Release 11.4, Junos OS supports restart signaling-based helper mode for OSPF graceful restart configurations.
Restart signaling-based graceful restart helper mode is not supported for OSPFv3 configurations.
Junos OS releases prior to Release 11.4 and OSPFv3 configurations support only standard helper mode as defined in RFC 3623 . For more information about the standard helper mode implementation, see RFC 3623 and the Junos OS High Availability Configuration Guide.
Both standard and restart signaling-based helper modes are enabled by default, irrespective of the graceful-restart configuration status on the device.
In restart signaling-based helper mode implementations, the restarting router informs the restart status to its neighbors only after the restart is complete. When the restart is complete, the restarting router sends hello messages to its helper routers with the restart signal (RS) bit set in the hello packet header. When a helper router receives a hello packet with the RS bit set in the header, the helper router returns a hello message to the restarting router. The reply hello message from the helper router contains the ResyncState flag and the ResyncTimeout timer that enable the restarting router to keep track of the helper routers that are syncing up with it. When all helpers complete the synchronization, the restarting router exits the restart mode.
For more information about restart signaling-based graceful restart helper mode implementation, see RFC 4811, OSPF Out-of-Band Link State Database (LSDB) Resynchronization, RFC 4812, OSPF Restart Signalingand RFC 4813, OSPF Link-Local Signaling.