Configuring IPFW Firewall on OS X
The latest versions of Mac OS X, being based on BSD style Unix, have a lot of powerful features that are legacy to many Unix operating systems. One is the ipfw firewall. OS X actually has two firewalls by default, an application firewall that blocks access to specific programs, and the ipfw firewall, which is a much lower level firewall that operates by inspecting inbound packets and allowing or denying them based on source IP, destination IP, port and protocol. This allows a much finer grain of control for remote access to an OS X computer.