This is a list of Internet socket port numbers used by protocols of the Transport Layer of the Internet Protocol Suite for the establishment of host-to-host communications.

Originally, these port numbers were used by the Network Control Protocol (NCP) and two ports were needed as transmission was done at half duplex. As TCP and UDP were adopted, only one port was needed. The even numbered ports were dropped. This is why the even numbers on well known port numbers are unassigned. Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) are also used for the Stream Control Transmission Protocol (SCTP), and the Datagram Congestion Control Protocol(DCCP). SCTP and DCCP services usually use a port number that matches the service 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.^[1] However, many unofficial uses of both well-known and registered port numbers occur in practice.

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[edit]Well-known ports

The port numbers in the range from 0 to 1023 are the well-known 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.

[edit]Registered ports

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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.^[1] On most systems, registered ports can be used by ordinary users.

This is an incomplete list of notable ports. See the Service Name and Transport Protocol Port Number Registry of IANA for the complete list of assigned ports.