Label Distribution Protocol
| application | LDP | ||||
| transport | UDP | TCP | |||
| Internet | IP ( IPv4 , IPv6 ) | ||||
| Network access | Ethernet |
Token bus |
Token ring |
FDDI | ... |
The Label Distribution Protocol (LDP) is a signaling protocol for establishing connections via Label Switched Path (LSP) in MPLS networks.
The protocol is used to negotiate labels and the associated forwarding classes between two label switch routers (LSR) or between a label switch router and a label edge router (LER).
Every LSR in an MPLS network periodically sends "Hello" packets via UDP port 646 as broadcast messages to all routers in the same subnet in order to make itself known in the network.
LDP sessions are established between knowing LSRs for bidirectional communication via TCP port 646 in order to exchange the MPLS labels and to get to know the respective forwarding class of the other router
LDP is scalable and can be easily expanded.
The protocol is standardized by the IETF and was first published in RFC 3036 . The current specification can be found in RFC 5036 .