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Determining Peer Reachability with RSVP-TE Hello Messages

RSVP-TE hello messages enable the router to detect when an RSVP-TE peer is no longer reachable. When the router makes this determination, all LSPs that traverse that neighbor are torn down. Hello messages are optional and can be ignored safely by peers that are not configured to use the feature.

When you enable the hello feature on a virtual router or interface configured with RSVP-TE, that RSVP-TE node periodically sends a unicast hello message to each neighbor with which the node has established an LSP. The exchange of hello messages between the peers establishes a hello adjacency. You can configure the hello interval to establish how frequently the node sends hello messages. Hello messages are exchanged when an LSP is set up and are stopped when the last LSP between the two peers goes away.

You can use the hello feature to reduce the impact of RSVP-TE on system resources. Because a hello timeout is treated as a link failure, RSVP-TE can use the hello timeout instead of path and resv timeouts to determine when to bring down an LSP. High RSVP-TE refresh values reduce the amount of control traffic (and CPU cycles) needed by RSVP-TE to refresh LSP state across the network, thus reducing the impact of RSVP-TE on system resources.

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