Label Distribution Protocol
computer network protocol
Label Distribution Protocol (LDP) is a protocol in which routers capable of Multiprotocol Label Switching (MPLS) exchange label mapping information. Two routers with an established session are called LDP peers and the exchange of information is bi-directional.
LDP is used to build and maintain label-switched path (LSP) databases that are used to forward traffic through MPLS networks.
LDP can be used to distribute the inner label (VC/VPN/service label) and outer label (path label) in MPLS. For inner label distribution, targeted LDP (tLDP) is used.
LDP and tLDP discovery runs on UDP port 646 and the session is built on TCP port 646. During the discovery phase hello packets are sent on UDP port 646 to the 'all routers on this subnet' group multicast address (224.0.0.2). However, tLDP unicasts the hello packets to the targeted neighbor's address.
LDP
The Label Distribution Protocol (LDP) is a protocol defined by the IETF (RFC 5036) for the purpose
of distributing labels in an MPLS environment. LDP relies on the underlying routing information provided by an IGP in order to forward label packets. The router forwarding information base, or FIB, is responsible for determining the
hop-by-hop path through the network.
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