this is a list of internet socket port numbers used by protocols of transport layer of the internet protocol suite for the establishment of host-to-host connectivity. originally, port numbers were used by the network control program (ncp) which needed two ports for half duplex transmission. later, transmission control protocol (tcp) and user datagram protocol (udp) needed only one port for bidirectional traffic (full duplex). the even-numbered ports were not used, and this resulted in some even numbers in the well-known port number range being unassigned. stream control transmission protocol (sctp) and datagram congestion control protocol (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. == table legend == {| class="wikitable" style="padding:2px;" |- ! use !! description !! color |- style="background:#f9f9f9;" | official || port is registered with iana for the application || white |- style="background:lightsteelblue;" | unofficial || port is not registered with iana for the application &nbsp; || blue |- style="background:khaki;" | multiple use ||multiple applications are known to use this port. || yellow |} == well-known ports == 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. {| class="wikitable sortable" |- ! port|| tcp || udp || description || status |- style="background:lightsteelblue;" | 0 || tcp || || programming technique for specifying system-allocated (dynamic) ports || unofficial |- | 0 || || udp || reserved || official |- | 1 || 
Computing-related_lists Internet-related_lists Internet_protocols Transmission_Control_Protocol