Take V300R019 as an example. Perform the following steps to solve the problem:
Run the start l2tp command on the LAC to check whether there is a reachable route to the LNS. If no, configure a reachable route to the LNS.
Check the L2TP configuration on the LNS and delete the parameter remote 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 either of the following methods to solve this problem:
Run the tunnel name command on the LAC to set the local tunnel name to the value of the parameter remote specified by the allow l2tp command on the LNS.
Run the allow l2tp command on the LNS to change the value of the parameter 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 the parameter remote is the device name of the LAC.
