Internet Guide Logo

Port

Last Edit: 10/01/17

Introduction

A port is a number used by software to serve as an end point communications address. Ports are used by Internet protocols (communications software) to identify a host. Generally speaking, an IP address and a port number are combined to locate a host. In relation to the Internet, the IP address locates a host computer, and the port number idenitifies an application running (such as a browser) on that host computer. The IP address can be likened to the address of a house, and the port number serves as an address to a room in that house.

Ports, in relation to the Internet, are typically used by the transport layer of the Internet protocol suite (TCP/IP). Transport layer protocols ensure that data packets - which are generated by application layer protocols (World Wide Web and Email etc) - are reliable sent and received. The two primary transport layer protocols are:

  1. Transmission Control Protocol (TCP)
  2. User Datagram Protocol (UDP)

Therefore, there are TCP port numbers and UDP port numbers; however, these numbers tend to be same for each specific application layer protocol. The Internet Assigned Numbers Authority (IANA) is the organisation that is responsible for assigning Internet numbers; which includes port numbers. Therefore, IANA define which TCP and UDP port number should be used by an application layer protocol.

Popular Port Numbers