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Configuring LDP and an IGP to Transport Layer 2 Circuits

 

LDP is used as the signaling protocol to advertise the ingress MPLS label to the remote PE router. For this purpose, a remote LDP neighbor is established using the extended discovery mechanism described in RFC 5036, LDP Specification, and a session is established.

No new configuration is necessary in LDP because the LDP protocol recognizes the Layer 2 circuit configuration and initiates extended neighbor discovery for all Layer 2 circuit neighbors on the remote PE routers. This is very similar to the behavior of LDP when it is tunneled over RSVP. However, you must configure LDP on the lo0.0 interface for extended neighbor discovery to function correctly.

LDP relies on an underlying IGP, such as OSPF or IS-IS. Therefore, configure LDP and your IGP on all routers in the path from the local PE router to the remote PE router across the service provider backbone.