LDP Overview
The Label Distribution Protocol (LDP) is a protocol for distributing labels in nontraffic-engineered applications. LDP allows routers to establish label-switched paths (LSPs) through a network by mapping network-layer routing information directly to data link layer-switched paths.
These LSPs might have an endpoint at a directly attached neighbor (comparable to IP hop-by-hop forwarding), or they might have an endpoint at a network egress node, enabling switching through all intermediary nodes. LSPs established by LDP can also traverse traffic-engineered LSPs created by RSVP.