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:PROPERTIES:
:ID: f4bb4857-2112-4e10-a22e-6da1436ce7b7
:END:
#+title: port
In computer networking, a port or port number is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system, a port is a logical construct that identifies a specific process or a type of [[id:c9461f7b-7368-4b88-b90b-2d785fda2159][network]] service. A port at the software level is identified for each transport [[id:bd5b34ba-aa98-4808-b97b-2376aa7b8866][protocol]] and address combination by the port number assigned to it. The most common transport protocols that use port numbers are the Transmission Control Protocol ([[id:0fa93c0d-6741-48cf-8bea-f2519146e4dc][TCP]]) and the User Datagram Protocol ([[id:b9c823ff-4cf4-46a0-8654-54bdc7b67d30][UDP]]); those port numbers are 16-bit unsigned numbers.
A port number is always associated with a network address of a host, such as an [[id:f055acfb-05dd-4228-a92a-356240b8c975][IP]] address, and the type of transport protocol used for communication. It completes the destination or origination address of a message. Specific port numbers are reserved to identify specific services so that an arriving [[id:fde35a08-897d-4502-aead-1f4414ea639c][packets]] can be easily forwarded to a running application. For this purpose, port numbers lower than 1024 identify the historically most commonly used services and are called the well-known port numbers. Higher-numbered ports are available for general use by applications and are known as ephemeral ports.
Ports provide a multiplexing service for multiple services or multiple communication sessions at one network address. In the [[id:70899526-8b7d-4976-94fc-cc07c41e550a][client]]–[[id:f2b1d5af-1a7d-47a5-95c8-4a85d558419e][server]] model of application architecture, multiple simultaneous communication sessions may be initiated for the same service.