3. Peer A receives the hello ack and sends another hello request to peer B. The
request object contains the following:
â– Source instance = 5 (generated by Peer A for this adjacency)
â– Destination instance = 8 (the source instance generated by Peer B for this
adjacency)
The two peers continue exchanging hello messages until the LSP is torn down. The
following is true for these message exchanges unless a peer resets:
â– Peer A always sends source instance= 5 and destination instance= 8 to Peer
B.
â– Peer B always sends instance= 8 and destination instance= 5 to Peer A.
Determination That a Peer Has Reset
After the initial exchange of hello messages, both peers perform checks on the
messages they receive to determine whether the peer has reset.
Behavior of the Requesting Peer
The requesting peer examines the ack messages it receives. It compares the source
instance in each subsequent ack message with the previous value. If the value differs
or is set to zero, then the requesting peer treats the acknowledging peer as if
communication has been lost.
The requesting peer also determines whether the acknowledging peer is reflecting
back the requesting peer’s source instance. If the acknowledging peer advertises a
wrong value in the destination instance field of the ack message, then the requesting
peer treats the acknowledging peer as if communication has been lost.
Behavior of the Acknowledging Peer
The acknowledging peer examines the request messages it receives. It compares the
source instance in each subsequent request message with the previous value. If the
value differs or is set to zero, then the acknowledging peer treats the requesting peer
as if communication has been lost.
The acknowledging peer also determines whether the requesting peer is reflecting
back the acknowledging peer’s source instance. It compares the destination instance
value in each request message with the source instance value that it most recently
advertised to the requesting peer. If the requesting peer advertises a wrong value in
the destination instance field of the request message, then the acknowledging peer
treats the requesting peer as if communication has been lost.
Behavior of Both Peers
When no hello messages are received from a peer within the configured hello interval,
the peer is treated as if communication has been lost.
Determining Peer Reachability with RSVP-TE Hello Messages â– 253
Chapter 2: MPLS Overview
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