When the NSR LDP Support feature is disabled, the active LDP performs the following tasks:
•
Stops checkpointing to the standby LDP
•
Continues to manage all existing sessions
The standby LDP performs the following tasks:
•
Cleans up all session-state information
•
Reverses to the behavior before NSR is enabled
LDP Operating States
When the NSR LDP Support feature is enabled, the Label Distribution Protocol (LDP) operates in the following
states:
Initial State
In the initial state, the active Label Distribution Protocol (LDP) process sets up the standby LDP to be ready
to support nonstop routing (NSR). The active LDP performs the following tasks:
•
Replicates all TCP sessions used by LDP with the standby LDP
•
Synchronizes all existing session-state information with the standby LDP
•
Synchronizes the LDP database with the standby LDP
LDP could be in the initial state because of one of these conditions:
•
NSR is enabled
•
NSR was enabled and the standby Route Processor (RP) starts up (asymmetric startup)
•
System boots up and NSR is configured (symmetric startup)
Steady State
In the steady state, the active and standby Label Distribution Protocol (LDP) databases are synchronized. The
active and standby LDP process the same LDP messages and update their states independently. The standby
LDP is ready to take over the active LDP role in a switchover event.
On the active Route Processor (RP), the active LDP performs the following tasks:
•
Continues to manage all existing sessions and checkpoints any significant session event to the standby
LDP (such as adjacency delete, session shutdown, timers)
•
Notifies the standby LDP of new adjacencies and neighbors
On the standby RP, the standby LDP performs these tasks:
•
Processes all received messages but does not send any messages to its neighbor
•
Processes checkpoint information from the active LDP
MPLS Basic Configuration Guide, Cisco IOS XE Everest 16.5.1 (Cisco ASR 900 Series)
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NSR LDP Support
LDP Operating States
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