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Typically, each computer on the Internet has a single physical connection to the network. However, a computer may have several applications that use data sent over that single physical connection. There must be a way of identifying which data is associated with which application. This is done by means of ports. A port is a connection point identified by a port number.

Typically, a specific application, such as a web server or a telnet service, will grab a particular port and expect clients to connect to that port in order to use the service provided by that application. Conventions have been set up to standardize port numbers for such applications.

Port Numbers

Port numbers are assigned by the Internet Assigned Numbers Authority (IANA), and are divided into three ranges: the Well Known Ports, the Registered Ports, and the Dynamic and/or Private Ports.