As of Mac OS X v10.5.1, Apple has included an application firewall as part of the OS. This level of protection is enabled by default and runs on top of the standard ipfw port-level firewall that has been part of the FreeBSD OS on which Mac OS X is based. While the default ipfw configuration 'out-of-the-box' is minimal, it is user-configurable and affords a two layer protection scheme.