Announcement of the Graceful Restart Capability

LSRs use the RSVP-TE hello mechanism to announce their graceful restart capabilities to their peer RSVP-TE routers. Both restarting LSRs and helper LSRs include the restart_cap object in hello requests and hello acks. The restart_cap object specifies both the graceful restart time and the graceful restart recovery time:

• restart time—The sum of how long it takes the sender to restart RSVP-TE after a control plane failure plus how long it takes to reestablish hello communication with the neighboring RSVP-TE routers.
• recovery time—The period within which you want neighboring routers to resynchronize with the sending router’s RSVP-TE state and MPLS forwarding state after the peers have re-established hello communication. The restarting LSR advertises the configured or default recovery time only while the graceful restart is in progress. When the LSR is not currently restarting or when it is incapable of preserving its MPLS forwarding state during the restart, the LSR advertises a recovery time of zero.

Both the restarting router and neighboring GR helper routers save the restart and recovery times that they receive from their peers.

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