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Recovery Behavior

In the recovery period, neighboring helper routers and the restarting router resynchronize the RSVP-TE state and MPLS forwarding state. During this period, MPLS traffic continues to be forwarded.

The helper router starts the recovery procedure by marking as stale the RSVP-TE state associated with the restarting router. The upstream helper router then refreshes all the path messages shared with the downstream restarting router. The upstream helper router includes the recovery_label object in the path message to the downstream restarting router for the label binding information that the restarting router specified before the restart. The downstream helper router does not refresh the reservation state control block (RSB) shared with the restarting router until a corresponding path message is received from the restarting router.

During the recovery period, the restarting router checks for the state associated with an incoming path message. If the RSVP-TE state already exists, the restarting router handles the path message as usual. Otherwise, the restarting router examines the path message for the recovery_label object. If the recovery_label object is not found, the restarting router treats the path message as a setup request for a new LSP and handles the path message as usual.

If the recovery_label object is found, the restarting router searches for the outgoing label based on the incoming interface and incoming label that are specified in the recovery_label object. If the restarting router does not find a match for the forwarding entry, the restarting router treats the path message as a setup request for a new LSP. If the restarting router finds a match, it conveys to the downstream neighbors the outgoing label associated with the forwarding entry in the suggested_label object in the path message and it continues normal operations.

The helper router removes the stale flag for the RSVP-TE state when it receives the corresponding state in path or resv messages sent by the restarting router. When the recovery period expires, the helper router deletes any RSVP-TE states that still have a stale flag. Graceful restart is considered to be complete when the recovery period expires or when the last LSP needing recovery is recovered.

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