RSVP Graceful Restart Operation

For RSVP graceful restart to function, the feature must be enabled on the global routing instance. RSVP graceful restart can be disabled at the protocol level (for RSVP alone) or at the global level for all protocols.

RSVP graceful restart requires the following of a restarting router and the router’s neighbors:

• For the restarting router, RSVP graceful restart attempts to maintain the routes installed by RSVP and the allocated labels, so that traffic continues to be forwarded without disruption. RSVP graceful restart is done quickly enough to reduce or eliminate the impact on neighboring nodes.
• The neighboring routers must have RSVP graceful restart helper mode enabled, thus allowing them to assist a router attempting to restart RSVP.

An object called Restart Cap that is sent in RSVP hello messages advertises a node’s restart capability. The neighboring node sends a Recover Label object to the restarting node to recover its forwarding state. This object is essentially the old label that the restarting node advertised before the node went down.

The following lists the RSVP graceful restart behaviors, which vary depending on the configuration and on which features are enabled:

• If you disable helper mode, the JUNOS software does not attempt to help a neighbor restart RSVP. Any information that arrives with a Restart Cap object from a neighbor is ignored.
• When you enable graceful restart under the routing instance configuration, the router can restart gracefully with the help of its neighbors. RSVP advertises a Restart Cap object (RSVP RESTART) in hello messages in which restart and recovery times are specified (neither value is 0).
• If you explicitly disable RSVP graceful restart under the [protocols rsvp] hierarchy level, the Restart Cap object is advertised with restart and recovery times specified as 0. The restart of neighboring routers is supported (unless helper mode is disabled), but the router itself does not preserve the RSVP forwarding state and cannot recover its control state.
• If after a restart RSVP realizes that no forwarding state has been preserved, the Restart Cap object is advertised with restart and recovery times specified as 0.
• If graceful restart and helper mode are disabled, RSVP graceful restart is completely disabled. The router neither recognizes nor advertises the RSVP graceful restart objects.

You cannot explicitly configure values for the restart and recovery times.

Unlike other protocols, there is no way for RSVP to determine that it has completed a restart procedure, other than a fixed timeout. All RSVP graceful restart procedures are timer-based. A show rsvp version command might indicate that the restart is still in progress even if all RSVP sessions are back up and the routes are restored.

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