RSVP refresh reduction

RSVP control traffic (Path and Resv messages) is initially propagated to establish an RSVP session and reserve resources along the path, or to signal a change of state (trigger messages). However, because it is a soft-state protocol, RSVP also requires periodic refreshing to prevent reserved resources from aging out. The original RSVP as defined in RFC 2205 achieves this by re-sending identical Path and Resv messages (refresh messages) at regular intervals along the reserved path as long as the RSVP session remains unchanged. The bandwidth and processing time required to support these refresh messages increases linearly as more RSVP sessions are established, which can result in scaling problems.

RFC 2961 establishes extensions to RSVP which can help reduce the overhead caused by refresh messages: bundle messages, which allows multiple RSVP messages to be aggregated into a single PDU, and summary refresh messages, which replace identical RSVP message re-transmissions with a list of the IDs of all Path and Resv states to be refreshed.

When the user enables either of the refresh reduction extensions on an interface, outgoing RSVP packets sent on that interface sets the refresh reduction capability bit in the common RSVP header to indicate that the device is capable of receiving and processing refresh reduction messages and related objects.