The establishment of pseudowires in LDP-signaled L2VPNs is accomplished by PE devices through the use of the Label Distribution Protocol. LDP is responsible for constructing, advertising, maintaining, and deleting label bindings for pseudowires.
PE devices exchange Targeted Hello messages to locate and establish LDP sessions, or adjacencies, with other PE devices. One such session, or adjacency, is shown in Targeted LDP adjacency.
Peer LDP speakers on peer PEs establish a TCP-based communications session with each other. Once the session is established, tunnel label data can be exchanged to construct pseudowires.
The MPLS Topology Server discovers the LDP speakers and LDP sessions that are associated with pseudowires. The MPLS Topology Server also discovers the LDP speakers and LDP sessions that are associated with LDP LSPs, as described in “More about LDP adjacencies and LDP adjacency discovery” on page 67.