Label Distribution Protocol (LDP) is a control protocol that functions like a signaling protocol on traditional networks. LDP classifies forwarding equivalence classes (FECs), distributes labels, and establishes and maintains label switched paths (LSPs). LDP defines messages used in the label distribution process as well as procedures for processing these messages.
MPLS is highly scalable because it allows multiple labels to be carried on a packet and has a connection-oriented forwarding plane. Scalability enables MPLS/IP networks to provide various services. Label switching routers (LSRs) on MPLS networks use the LDP protocol to map Layer 3 routing information to Layer 2 switched paths, and establish LSPs at network layers.
LDP is widely used to provide virtual private network (VPN) services due to simple deployment and configuration, ability to establish LSPs dynamically based on routing information, and ability to support many LSPs.