Two LSRs that use LDP to establish an LDP session and exchange label messages are called LDP peers. LDP peers learn labels from each other over the LDP session between them.
Local adjacency
Discovered by multicasting a Hello message (Link Hello message).
Remote adjacency
Discovered by unicasting a Hello message (Targeted Hello message).
LDP maintains peer information based on adjacencies. The peer type is defined by the type of LDP adjacency. A peer can be maintained by multiple adjacencies. If a peer is maintained by both local and remote adjacencies, the peer type is coexistent local and remote.
LSRs exchange messages, such as label mapping and release messages, over LDP sessions. LDP sessions are only established between LDP peers. LDP sessions are classified into the following types:
Local LDP session
Established between two directly connected LSRs.
Remote LDP session
Established between two directly or indirectly connected LSRs.
The local and remote LDP sessions can coexist.