FreeBSD® Unleashed

Using a Firewall

It's undeniable that firewalls, or machines that operate as routers with filters, are an increasingly important—even indispensable—part of maintaining an Internet server. Easily accessible hacking tools, run incessantly by “script kiddies” with nothing better to do, make it imperative that you have some kind of protection layer beyond simply electing not to run certain services and keeping on top of security bulletins. You need a generalized shield at the kernel level that prevents your system from being accessed at all on certain ports, from certain hosts, or over certain protocols. Firewalls, particularly the IPFW firewall that comes with FreeBSD, are an answer to this need.

A firewall can prevent the vast majority of casual ...