Basic Concepts
LDP Peers
Two LSRs that use LDP to set up an LDP session and exchange label messages are LDP peers.
LDP peers learn labels from each other over the LDP session between them.
LDP Adjacency
Local adjacency: adjacency discovered by multicasting a Hello message (link Hello message)
Remote adjacency: adjacency discovered by unicasting a Hello message (targeted Hello message)
LDP maintains peer information based on adjacencies. The type of a peer depends on the type of its adjacency. A peer can be maintained by multiple adjacencies. If a peer is maintained by both local and remote adjacencies, the peer is a local-and-remote peer.
LDP Session
LSRs exchange messages over an LDP session that include label mapping and release messages. LDP sessions can be set up only between LDP peers. The following types of LDP sessions are available:
Local LDP session: set up between two LSRs that are directly connected
Remote LDP session: set up between two LSRs that are directly or indirectly connected
An LSR can set up local and remote LDP sessions simultaneously.