In the Internet Protocol (IP) [RFC791] there is a field to identify the version of the internetwork general protocol. This field is 4 bits in size.
Assigned Internet Version Numbers
Decimal Keyword Version References ------- ------- ------- ---------- 0 Reserved [JBP] 1-3 Unassigned [JBP] 4 IP Internet Protocol [RFC791,JBP] 5 ST ST Datagram Mode [RFC1190,JWF] 6 IPv6 Internet Protocol version 6 [RFC1752] 7 TP/IX TP/IX: The Next Internet [RXU] 8 PIP The P Internet Protocol [PXF] 9 TUBA TUBA [RXC] 10-14 Unassigned [JBP] 15 Reserved [JBP]
[RFC791] Postel, J., ed., "Internet Protocol - DARPA Internet Program Protocol Specification", STD 5, RFC 791, USC/Information Sciences Institute, September 1981.
[RFC1190] Topolcic, C., Editor, "Experimental Internet Stream Protocol, Version 2 (ST-II)", RFC 1190, CIP Working Group, October 1990.
[RFC1752] Bradner, S., and A. Mankin, "The Recommendation for the IP Next Generation Protocol", RFC 1752, Harvard University, ISI, January 1995.
[JPB] Jon Postel <email@example.com>
[JWF] Jim Forgie <FORGIE@XN.LL.MIT.ED>
[RH6] Robert Hinden <Hinden@ENG.SUN.COM>
[RXU] Robert Ullmann <firstname.lastname@example.org>
[PXF] Paul Francis <email@example.com>
[RXC] Ross Callon <firstname.lastname@example.org>
[Deering] Steve Deering, <email@example.com>, March 1995.
My name is Michael Oliver, and I
can be contacted by email here.