Tere.

If you're using PAM authentication then just use pam_group to restrict it to a specific group.

I'm using pam, but how to use this pam_group to allow connect all users from my networks a'la 192.168.0.0/24 and only some users from other network a'la 0.0.0.0 to connect to the port 993?

-- Sysadmin