RSVP messages
RSVP uses the following types of messages:
Path messages—Sent by the sender downstream along the data transmission path to save path state information on each node along the path.
Resv messages—Sent by the receiver upstream towards the sender to request resource reservation and to create and maintain reservation state on each node along the reverse data transmission path.
PathTear messages—Sent downstream by the sender or a transit node to remove the path state and related reservation state on each node along the path.
ResvTear messages—Sent upstream by the receiver or a transit node to remove the reservation state on each node along the path.
PathErr messages—Sent upstream by the receiver or a transit node to report Path message processing errors to the sender. They do not affect the state of the nodes along the path.
ResvErr messages—Sent downstream by the sender or a transit node to notify the downstream nodes of an Resv message processing error or of a reservation error caused by preemption.
ResvConf messages—Sent to the receiver to confirm Resv messages.
Hello messages—Sent between any two directly connected RSVP neighbors to set up and maintain the neighbor relationship. Hello messages are sent only when the RSVP hello extension has been enabled.
RSVP-TE extends RSVP by adding new objects to Path and Resv messages. In addition to label bindings, these objects also carry routing constraints to support CRLSP and FRR.
New objects added to the Path message:
LABEL_REQUEST—Requests the downstream node to allocate a label.
EXPLICIT_ROUTE—Carries the path information calculated by the ingress node, making sure the CRLSP is set up along that path.
RECORD_ROUTE—Records the path that the CRLSP actually traverses and the label allocated by each node on the path.
SESSION_ATTRIBUTE—Carries the MPLS TE tunnel attributes, such as the setup priority, holding priority, and affinity.
New objects added to the Resv message:
LABEL—Advertises the label allocated by the downstream node to the upstream node.
RECORD_ROUTE—Records the path that the CRLSP actually traverses and the label allocated by each node on the path.