Question

An engineer enables LDP on all core interfaces of a service provider MPLS network. Two directly connected LSRs, P1 and P2, form an LDP session, but it repeatedly flaps. On P1, 'show mpls ldp neighbor' shows the peer LDP ID as the physical interface address rather than a loopback. P1 has a loopback0 (10.0.0.1/32) advertised in the IGP, but P2 cannot reach it because the /32 is filtered by an IGP prefix-list. Which action will produce a stable LDP session between P1 and P2?

Accepted Answer

Ensure the LDP router-ID loopback (/32) used by each LSR is reachable in the IGP, since the LDP TCP session is established to the LDP router-ID address

Answer

Configure 'mpls ldp discovery transport-address interface' so LDP uses only the directly connected physical interface addresses

Answer

Enable 'mpls ip' on the loopback0 interface of both P1 and P2 so labels are allocated for the router-ID

Answer

Change the LDP label protocol to TDP so the session no longer depends on loopback reachability