Port Numbers

A Port Number does not describe a physical port such as a LAN or WAN port but rather a logical port used to keep track of a specific process on the network. Various processes and services on networks and across the Internet are associated with port numbers. For example, the FTP process used by the FTP server on the IT-100 uses ports 20 and 21. DNS uses port 53 and HTTP (web) uses port 80. Port numbers become important when you are trying to customize the firewall on the IT-100, since you will need to know the port number of services you are trying to allow or deny. There are literally tens of thousands of port numbers but you may only occasionally need to know a few in order to perform a firewall configuration. Each process defined by a port number either uses transport protocols TCP, UDP, or both. For more information, see the terms DNS, FTP, HTTP, TCP, and UDP in this Glossary.