IPFilter (commonly referred to as ipf) is an open-source software package that provides firewall services and network address translation (NAT) for many Unix-like operating systems. The author and software maintainer is Darren Reed. IPFilter supports both IPv4 and IPv6 protocols, and is a stateful firewall. IPFilter can be installed as a runtime-loadable kernel module or directly incorporated into the operating system kernel, depending on the specifics of each kernel and user preferences. The software's documentation recommends the module approach, if possible.