LDP timers include the target Hello hold timer, target Hello send timer, Keepalive hold timer, Keepalive send timer, and Exponential backoff timer.
Target Hello send timer: An LSR sends Hello messages to a peer LSR at an interval specified by the Hello send timer. The LSR can advertise its existence and establish a Hello adjacency with the peer LSR.
Target Hello hold timer: LDP peers that establish a Hello adjacency periodically exchange Hello messages indicating that they expect to maintain the adjacency. If the Hello hold timer expires and no Hello messages are received, the Hello adjacency is torn down.
Keepalive send timer: LSRs on both ends of an established LDP session start Keepalive send timers and periodically exchange Keepalive messages to maintain the LDP session.
Keepalive hold timer: LDP peers start Keepalive hold timers and periodically send LDP PDUs over an LDP session connection to maintain the LDP session. If the Keepalive hold timers expire and no LDP PDUs are received, the connection is closed, and the LDP session is torn down.
Exponential backoff timer: An active LSR starts this timer after it fails to process an LDP Initialization message or after it receives the notification that the passive LSR to which the active LSR sends the LDP Initialization message has rejected the parameters carried in the message. The active LSP periodically resends an LDP Initialization message to initiate an LDP session before the Exponential backoff timer expires.
The default timer values are recommended.