Why is the LDP GR duration in the log longer than 10 minutes, which is the interval of the MPLS Forwarding State Holding timer

4

After the GR restarter performs an active/standby switchover, LDP GR starts only after route GR is complete. The MPLS Forwarding State Holding timer is started immediately after the active/standby switchover but restarted when route GR is complete. In the log, the GR begin time is the time when the MPLS Forwarding State Holding timer is first started; the GR end time is the time when the MPLS Forwarding State Holding timer expires. Therefore, the LDP GR duration recorded in the log is the sum of the route GR duration and MPLS Forwarding State Holding timer interval (10 minutes).

Other related questions:
What are the default intervals of the GR timers in the MPLS LDP view
The default interval of the MPLS Forwarding State Holding timer (Neighbor-liveness timer) is 10 minutes. The default intervals of the GR Reconnect timer and GR Recovery timer are both 5 minutes.

What functions do GR timers provide in the MPLS LDP view
After GR Restarter performs an active/standby switchover, the MPLS Forwarding State Holding Timer is started, which is the Neighbor-liveness timer in the MPLS LDP view. Before the Neighbor-liveness timer expires, all forwarding entries before the active/standby switchover are retained. After the Neighbor-liveness timer expires, the GR Helper deletes the forwarding entries that are not restored. When detecting that the GR Restarter performs an active/standby switchover or the LDP protocol restarts, the GR Helper starts the GR Reconnect timer. Before the GR Reconnect timer expires, the GR Helper retains all forwarding entries related to the GR Restarter. After the GR Reconnect timer expires, the GR Helper deletes the forwarding entries that are not restored. If a session is re-established between the GR Restarter and Helper before the GR Reconnect timer expires, the GR Helper deletes the GR Reconnect timer and starts the GR Recovery timer. Before the GR Recovery timer expires, the GR Helper helps the GR Restarter restore forwarding entries. After the GR Recovery timer times out, the GR Helper deletes all the GR Restarter-related forwarding entries that are not restored.

How to set the durations of the Hold timer and Keepalive timer of the BGP peer
You can run the peer timer command to set the durations of the Hold timer and Keepalive timer. This command specifies the timeout period of the BGP connection and the interval to send the Keepalive message. A longer timeout period can relieve the impact of link flapping, whereas a shorter timeout period makes the timer rapidly perceive link changes. After connections are established between two peers, the durations of the two timers are negotiated by the two peers and the shorter durations are adopted.

How to troubleshoot the fault of LDP session flapping due to the expiration of Hello Hold timer
If the Hello Hold timer expires, run the display mpls ldp interface command to check whether Hello messages are properly sent on the two ends of the LDP session. If not, the system is busy or faulty. If Hello messages are properly sent but the peer end does not receive them, ping the address of the peer end to check the forwarding status.

How to troubleshoot the fault of LDP session flapping due to the expiration of KeepAlive Hold timer
If the KeepAlive Hold timer expires, run the display mpls ldp session command to check whether KeepAlive messages are properly sent on the two ends of the LDP session. If not, the system is busy or faulty. If KeepAlive messages are properly sent but the peer end does not receive them, ping the transport address of the TCP connection with the peer end to check the forwarding status.

If you have more questions, you can seek help from following ways:
To iKnow To Live Chat
Scroll to top