Terminology

Two LSRs establish a TCP-based LDP session to exchange FEC-label mappings.

Two LSRs that use LDP to exchange FEC-label mappings are LSR peers.

Label spaces include the following types:

• Per-interface label space—Each interface uses a single, independent label space. Different interfaces can use the same label values.

• Per-platform label space—Each LSR uses a single label space. The device only supports the per-platform label space.

A six-byte LDP Identifier (LDP ID) identifies a label space on an LSR. It is in the format of <LSR ID>:<label space number>, where the LSR ID takes four bytes to identity the LSR, and the label space number takes two bytes to identify a label space within the LSR. A label space number of 0 indicates that the label space is a per-platform label space. A label space number other than 0 indicates a per-interface label space.

MPLS groups packets with the same characteristics (such as the same destination or service class) into a class, called an FEC. The packets of the same FEC are handled in the same way on an MPLS network.

LDP can classify FECs by destination IP address and by PW. This document describes FEC classification by destination IP address. For information about FEC classification by PW, see "Configuring MPLS L2VPN" and "Configuring VPLS."

An LSR assigns a label for an FEC and advertises the FEC-label mapping, or FEC-label binding, to its peers in a Label Mapping message.