A TCP/IP port is a "logical connection place." Using the Internet protocol, TCP/IP, a port enables a client program to specify a particular server program on a computer in a network. Higher-level applications that use TCP/IP, such as Hypertext Transfer Protocol (HTTP), have port numbers that are pre-assigned by the Internet Assigned Numbers Authority (IANA), which are called "well known ports." Other application processes are assigned port numbers dynamically for each connection. When a service (or server program) is started initially, it is said to "bind" to its designated port number. Any client program that wants to use that server must send a request to bind to the designated port number.
Port numbers are between 0 and 65536. Ports 0 to 1024 are reserved for use by certain privileged services. For the HTTP service, port 80 is the default and does not have to be specified in the Uniform Resource Locator (URL).
Copyright 2001 Sun Microsystems, Inc. All rights reserved. Legal Notice.