MPLS FIB

Periodically, I have to refigure out the correct terminology for an “MPLS FIB”, label FIB, or LFIB. For my future self, and anyone else, the appropriate name is the “Incoming Label Map”, and the reference is RFC 3031 section 3.11.

3.11. Incoming Label Map (ILM)

The “Incoming Label Map” (ILM) maps each incoming label to a set of NHLFEs. It is used when forwarding packets that arrive as labeled packets.

If the ILM maps a particular label to a set of NHLFEs that contains more than one element, exactly one element of the set must be chosen before the packet is forwarded. The procedures for choosing an element from the set are beyond the scope of this document. Having the ILM map a label to a set containing more than one NHLFE may be useful if, e.g., it is desired to do load balancing over multiple equal-cost paths.