How to rapidly locate the cause of a failure to establish a tunnel between the LAC and LNS

During L2TP configuration, the LAC cannot set up a tunnel with the LNS. Perform the following operations to quickly locate the fault.
1. Run the start l2tp command on the LAC to check whether there is a reachable route to the LNS. If the route is unreachable, ensure route reachability.
2. Check the L2TP configuration on the LNS and delete the remote parameter specified in the allow l2tp command. If an L2TP tunnel can be established successfully, the LAC cannot set up a tunnel with the LNS because the tunnel name on the LAC is incorrect or the tunnel name specified by the LNS is incorrect. Use the following methods:
 - Run the tunnel name command on the LAC to set the local tunnel name to the value of remote specified by the allow l2tp command on the LNS.
 - Run the allow l2tp command on the LNS to change the value of remote to the tunnel name configured on the LAC. If no local tunnel name is configured using the tunnel name command on the LAC, the value of remote is the device name of the LAC.

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