Common Internet Ports & Services

Although most people dont know about it but the internet works on various ports. Think of it almost like a whole bunch of telephone lines, with each line providing a service, for instance port 80 lets you see web pages, port 22 allows you to telnet into machines. Each port being a different way to communicate. I find knowing the ports of most commonly used programs and services is useful in detecting intrusions or for restricting your firewall.