This tiny program terminates all TCP connections which are not from a trusted source.
pmtfw [-f] [-i dev] -a AllowedIP1,AllowedIP2,...,AllowedIPN
-f : stay in foreground
-i DEV : only filter traffic on interface DEV
-a LIST : comma separated list of allowed IPs
-h : show help
Q: Which operation systems are supported?
A: The program is designed to run on GNU/Linux but porting it to any other UNIX should be easy.
Q: Why should I use this tool?
A: It was written to allow minimal firewalling on embedded systems where no iptables or hosts.{allow,deny} files are available. The author is using it to have firewalling on crappy IPMI devices.