Maintaining L2TP

After configuring L2TP, you can perform tunnel authentication and maintenance. If the tunnel authentication succeeds, the established tunnel can be used properly. If the tunnel authentication fails, troubleshoot the fault based on common L2TP VPN troubleshooting methods.

Checking the running status of L2TP

You can run the commands listed in Table 1 in any view to view the running status of L2TP.

**Table 1** Checking the running status of L2TP
Operation	Command
Check L2TP session information.	display l2tp session [ slot slot-id cpu cpu-id ]
Check L2TP tunnel information.	display l2tp tunnel [ slot slot-id cpu cpu-id ]
Check brief information about all online users.	display access-user
Check the main configurations of the VT interface.	display interface virtual-template virtual-template-number

Forcibly Closing Tunnel Connections

When there is no L2TP user, a network fault occurs, or the administrator wants to close a tunnel, tunnel clearing is required. Running the reset command clears the control connections and sessions over tunnels. Clearing tunnels interrupts services. When a new user initiates a dialup request, a tunnel can be reestablished. Both the LAC and LNS can initiate a request for clearing a tunnel. The device that receives the request sends an ACK message and waits a specific period to clear the tunnel so that the device can receive the request retransmitted by the other device if the ACL message is lost.

You can run the commands listed in Table 2 to forcibly close L2TP tunnel connections in the user view.

**Table 2** Forcibly closing specific tunnel connections
Operation	Command
Forcibly closing a specific L2TP connection.	reset l2tp tunnel { tunnel-item tunnel-id \| tunnel-name tunnel-name } [ slot slot-id cpu cpu-id ]
Forcibly closing all L2TP connections.	reset l2tp tunnel all [ all-systems \| vpn-instance vpn-instance ]

Debugging L2TP

When an L2TP running fault occurs, run debugging commands in the user view to debug L2TP, view the debugging information, and locate and analyze the fault.

Before enabling the debugging function, you must run the terminal monitor and terminal debugging commands in the user view to enable the information display and debugging information display functions of the terminal.

Debugging commands degrade system performance. After debugging, run the undo debugging all command to disable the debugging function immediately.