Well-known port

This is a list of Internet socket port numbers used by protocols of the transport layer of the for the establishment of host-to-host connectivity.

Originally, port numbers were used by the Network Control Program (NCP) in the ARPANET for which two ports were required for half-duplex transmission. Later, the (TCP) and the (UDP) needed only one port for full-duplex, bidirectional traffic. The even-numbered ports were not used, and this resulted in some even numbers in the well-known port number range being unassigned. The (SCTP) and the (DCCP) also use port numbers. They usually use port numbers that match the services of the corresponding TCP or UDP implementation, if they exist.

The Internet Assigned Numbers Authority (IANA) is responsible for maintaining the official assignments of port numbers for specific uses. However, many unofficial uses of both well-known and registered port numbers occur in practice.

The port numbers in the range from 0 to 1023 are the well-known ports or system ports. They are used by system processes that provide widely used types of network services. On Unix-like operating systems, a process must execute with superuser privileges to be able to bind a network socket to an IP address using one of the well-known ports.

The range of port numbers from 1024 to 49151 are the registered ports. They are assigned by IANA for specific service upon application by a requesting entity. On most systems, registered ports can be used without superuser privileges.

The range 49152–65535 (2¹⁵+2¹⁴ to 2¹⁶−1) contains dynamic or private ports that cannot be registered with IANA. This range is used for private, or customized services or temporary purposes and for automatic allocation of ephemeral ports.

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