A much more common use of iptables for me is to limit outside traffic to port 21, 80, and 447, while letting whitelisted internal hosts use every other ports, f

A much more common use of iptables for me is to limit outside traffic to port 21, 80, and 447, while letting whitelisted internal hosts use every other ports, for other services used internally. We can then run those services without authentication, and have much less exposure in case of an attack (the only thing whose security we must trust is iptables, ssh, our HTTP web server.)