Assigned Numbers

For compatibility with the general network environment, well-known numbers are assigned for the Internet versions, networks, ports, protocols, and protocol options. Additionally, well-known names are also assigned to machines, networks, operating systems, protocols, services, and terminals.

TCP/IP complies with the assigned numbers and names defined in RFC 1010, Assigned Numbers.

The Internet Protocol (IP) defines a 4-bit field in the IP header that identifies the version of the general Internetwork protocol in use. For IP, this version number in decimal is 4. For details on the assigned numbers and names used by TCP/IP, see /etc/protocols and /etc/services files included with TCP/IP. For further details on the assigned numbers and names, refer to RFC 1010 and the /etc/services file.