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Restarting Behavior

When the control plane fails, the LSR stops sending hello messages to its RSVP-TE neighbors. However, as a restarting router the LSR can continue to forward MPLS traffic because it preserves its MPLS forwarding state during the restart. When RSVP-TE comes back up, the restarted router sends the first hello message to its neighbors with a new source instance value to indicate that it had a control plane failure. The destination instance value in the hello message is set to zero. The recovery time included in this hello message is set to zero only if the router was unable to preserve the MPLS forwarding state or to support control state recovery.

When a neighboring router that has been configured as a graceful restart helper determines that the number of continuous missing hellos has reached the configured hello miss limit, it declares the router to be down. The helper router then waits for a period equal to the restart time that it received from the router and stored before the failure. During this period, the helper router preserves the restarting router's RSVP-TE state and MPLS forwarding state for the established LSPs and keeps forwarding MPLS traffic. However, the helper router suspends the refreshing of path and resv state to the restarting router. The helper router keeps sending hello messages to the restarting router with an unchanged source instance value and a destination instance value set to zero. The helper router removes the RSVP-TE state for any LSP that was in the process of being established when the neighbor was declared to be down.

If the helper router does not receive a hello message from the restarting router during the restart period, the helper router immediately exits the recovery procedure and cleans up the states associated with the restarting router. The helper router determines that the failed neighbor has restarted when it finds a new source instance in the neighbor's hello message. When a nonzero recovery time is received in that hello message, the helper router determines that the restarted neighbor supports state recovery. The helper router then starts the recovery procedures. However, if the recovery time specified in the hello message is zero, then the helper router exits the recovery procedure and cleans up the states associated with the restarting router.

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