When an LSR receives a FEC-label binding from an LDP neighbor for a specific FEC1 element, the following procedures are performed.
LDP installs the FEC if:
It was able to perform a successful exact match or a longest match, if aggregate-prefix-match option is enabled in LDP, of the FEC /32 prefix with a prefix entry in the routing table.
The advertising LDP neighbor is the next-hop to reach the FEC prefix.
When such a FEC-label binding has been installed in the LDP FIB, LDP performs the following:
Program a push and a swap NHLFE entries in the egress data path to forward packets to FEC1.
Program the CPM tunnel table with a tunnel entry for the NHLFE.
Advertise a new FEC-label binding for FEC1 to all its LDP neighbors according to the global and per-peer LDP prefix export policies.
Install the ILM entry pointing to the swap NHLFE.
When BGP learns the LDP FEC by way of the CPM tunnel table and the FEC prefix exists in the BGP route export policy, it performs the following:
Originate a labeled BGP route for the same prefix with this node as the next-hop and advertise it by way of IBGP to its BGP neighbors, for example, the local ABR/ASBR nodes, which have the advertise-ldp-prefix enabled.
Install the ILM entry pointing to the swap NHLFE programmed by LDP.