The port numbers in the range from 0 to 1023 are the well-known ports. Multiple applications are known to use this port. Port is not registered with IANA for the application Port is registered with IANA for the application However, many unofficial uses of both well-known and registered port numbers occur in practice. The Internet Assigned Numbers Authority (IANA) is responsible for maintaining the official assignments of port numbers for specific uses. SCTP and DCCP services usually use a port number that matches the service of the corresponding TCP or UDP implementation if they exist. 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). This is why the even numbers on well known port numbers are unassigned. As TCP and UDP were adopted, only one port was needed. Originally, these port numbers were used by the Network Control Protocol (NCP) and two ports were needed as transmission was done at half duplex. 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.
