MPLS: LDP

LDP uses Hello messages to determine neighbors and maintain up status with neighbors.  LDP multicasts to 224.0.0.2 using UDP port 646 for LDP.  Older TDP uses UDP port 711.

Hellos contain a 32 bit dot decimal number and 2 byte label space number referred to as a LSR LDP ID (LID)

LSRs can optionally send a transport address in the Hello messages to allow neighbors to send any TCP communications to work.  If a transport address is not used, hosts will use the IP address in the first 4 bytes of the LDP ID for TCP connections

Once neighbors are found they establish a TCP connection using TCP 646 (or older TCP 711 for TDP).  Once a connection is up each router advertises its list of local labels and prefix bindings.

 

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