What is a computer network port?
A port in computer networking is how a computer can use a single physical network connection to handle many incoming and outgoing requests by assigning a port number to each. The numbers go from 0 to 65535, which is a 16-bit number.
Some of these port numbers are specifically defined and always associated with a specific type of service — for example, File Transfer Protocol (FTP) is always port number 21 and Hypertext Transfer Protocol web traffic is always port 80. These are called well-known ports and go from 0 to 1023.
The numbers from 1024 to 49151 are called registered ports and can be registered with the Internet Assigned Numbers Authority for a specific use. The numbers 49152 to 65535 are unassigned, can be used by any type of service and are called dynamic ports, private ports or ephemeral ports.
As an illustration, think of a port number as a telephone extension in a business telephone system. The company telephone number is like the computer Internet Protocol (IP) address or Uniform Resource Locator (URL). It connects users with the correct company but does not define who they want to talk to in the company. A telephone extension will connect them with the right person in an organization, however, and the port will connect them to the right service on a computer. Dialing extension 0 to speak to an operator is extremely common in all phone systems and is like the well-known ports that always define specific services.