Question

A network engineer is documenting the control-plane behavior of an MPLS core running LDP on all P and PE routers. During a design review, a colleague asks how an LSR in a Cisco IOS MPLS network learns the labels it uses to reach an IGP prefix. Which statement correctly describes the default LDP label distribution and retention behavior?

Accepted Answer

Each LSR advertises a label binding for every prefix in its routing table to all LDP peers unsolicited, and retains all received bindings even from non-best-path neighbors.

Answer

An LSR requests a label for a prefix only from its downstream next-hop neighbor on demand, and discards any bindings not currently used for forwarding.

Answer

Labels are distributed only by the egress PE and flooded hop-by-hop upstream, with each transit LSR reusing the same label value end to end.

Answer

The ingress PE allocates a single global label for the entire LSP, and every transit LSR forwards based on that unchanged label until the egress PE.