Punch Through NAT with Port Map’s Port Forwarding
But NAT isn’t a brick wall, even though it’s often called a passive firewall. Most NAT-capable routers also include one of two standard methods of allowing software running on a computer with a private address to ask the router to open up a limited form of incoming access. Automatic port mapping protocols on the router open one or more ports—a kind of numbered slot that can be attached to an IP address—and hand the port number or numbers back to the requesting software. As long as the router itself has a publicly routable IP address that can be reached via the Internet, port-mapped applications can now be reached as well.
