You can configure the XTM device to host Mobile VPN with L2TP sessions. When the XTM device is configured for Mobile VPN with L2TP, users included in the Mobile VPN with L2TP group can use an L2TP client to make an L2TP connection.
Because the XTM device allows the L2TP connection from any of your users who give the correct credentials, it is important that you make sure that a policy for L2TP VPN sessions that includes only users you want to allow to send traffic over the L2TP VPN is included in your configuration. You can also add these users to a Firebox User Group and add a policy that allows traffic only from this group. The XTM device creates a pre-configured group called L2TP-Users for this purpose.
To configure a Mobile VPN with L2TP connection:
Use the WatchGuard L2TP Setup Wizard
Certificates for Mobile VPN with L2TP Tunnel Authentication