RSVP Refresh Reduction
RSVP relies on soft-state to maintain the path and reservation states on each router. If the corresponding refresh messages are not sent periodically, the states eventually time out and reservations are deleted. RSVP also sends its control messages as IP datagrams with no reliability guarantee. It relies on periodic refresh messages to handle the occasional loss of Path or Resv messages.
The RSVP refresh reduction extensions, based on RFC 2961, addresses the following problems that result from relying on periodic refresh messages to handle message loss:
- Scalability—The scaling problem arises from the periodic transmission and processing overhead of refresh messages, which increases as the number of RSVP sessions increases.
- Reliability and latency—The reliability and latency problem stems from the loss of nonrefresh RSVP messages or one-time RSVP messages such as PathTear or PathErr. The time to recover from such a loss is usually tied to refresh interval and the keepalive timer.
The RSVP refresh reduction capability is advertised by enabling the refresh reduction (RR) capable bit in the RSVP common header. This bit is only significant between RSVP neighbors.
RSVP refresh reduction includes the following features:
- RSVP message bundling using the bundle message
- RSVP Message ID to reduce message processing overhead
- Reliable delivery of RSVP messages using Message ID, Message Ack, and Message Nack
- Summary refresh to reduce the amount of information transmitted every refresh interval
The RSVP refresh reduction specification (RFC 2961) allows you to enable some or all of the above capabilities on a router. It also describes various procedures that a router can use to detect the refresh reduction capabilities of its neighbor.
The Junos OS supports all of the refresh reduction extensions, some of which can be selectively enabled or disabled. The Junos OS supports Message ID and therefore can perform reliable message delivery only for Path and Resv messages.
For information about how to configure RSVP refresh reduction, see Configuring RSVP Refresh Reduction.
