A customer of mine uses a CN Force200 as cpe. I'm not able now to get access to his access point so my need is to block an user/intruder who gets connection. Could you kindly help me with CN L2 firewall application ? Lots of thanks in advance.
If I understand your original post you want a way to keep customers behind a SM to be able to login to the AP and make changes.
Have you considered using the Management Access feature? This can be found under Configuration > Network. The purpose is to make sure the AP can only be accessed via the Ethernet interface.