When the Keepalive Hold timer expires, you need to check whether both ends of the LDP session can normally send Keepalive messages by running the display mpls ldp session command. If Keepalive messages are not sent normally, the possible cause is that the system is busy or a fault occurs in the system. If Keepalive messages are normally sent but fail to be received, the possible cause is that the transmission on links is abnormal. In this case, you can ping the transport address used to set up a TCP connection on the peer to check the forwarding status.
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