Chapter 10 Install and System Administration for FortiOS 5.0 : PPTP and L2TP : Adding the security policy : Monitoring L2TP sessions
  
Monitoring L2TP sessions
You can display a list of all active sessions and view activity by port number. By default, port 1701 is used for L2TP VPN-related communications. If required, active sessions can be stopped from this view. Use the Top Sessions Dashboard Widget.
See Also
Configuring a Linux client
Testing L2TP VPN connections
Logging L2TP VPN events
Adding the security policy
PPTP and L2TP