More about LDP
adjacencies and LDP adjacency discovery
The establishment of LDP LSPs is accomplished by PE and P devices
through the use of the Label Distribution Protocol. LDP is responsible for
assigning tunnel labels to an LDP LSP and for handling error conditions.
An LDP LSP is PE to PE.
PE and P devices exchange LDP Link Hello messages to locate and
establish LDP sessions with their directly connected neighbors. Three such
sessions, or adjacencies, are shown in
Non-targeted LDP adjacencies.
Non-targeted LDP
adjacencies

Peer LDP speakers establish a TCP-based communications session with each
other. Once the session is established, tunnel label data can be exchanged to
construct LDP LSPs.
The
MPLS Topology Server
discovers the LDP speakers and LDP sessions that are associated with LDP LSPs.
The
MPLS Topology Server
also discovers the LDP speakers and LDP sessions that are associated with
L2VPNs, as described in
“More about targeted LDP
adjacencies and LDP adjacency discovery” on page 93.