Unlike most port numbers, port 0 is a reserved port in TCP/IP networks, which means it should not be used in TCP or UDP messages. Network ports in TCP and UDP range from the number 0 to 65535. Port numbers from 0 to 1023 are defined as non-temporary ports, system ports or known ports. The Internet Assigned Numbers Authority (IANA) maintains an official list of the intended uses of these port numbers on the Internet and does not use system port 0.