List of IP version numbers

Packets that hold Internet Protocol data carry a 4-bit IP version number as the first field of its header.[1][2] Currently, only IPv4 and IPv6 packets are seen on the Internet, having IP version numbers 4 and 6, respectively.

IP version numbers

As the version number is carried in a 4-bit field, only numbers 0–15 can be assigned.

IP version	Description	Status
0	Internet Protocol, pre-v4	Reserved.[3]
1–3		Unassigned.
4	Internet Protocol version 4 (IPv4)[1]	Active.
5	Internet Stream Protocol or ST	Obsolete; superseded by ST-II.
5	Internet Stream Protocol or ST-II[4]	Obsolete.
6	Simple Internet Protocol (SIP)	Obsolete; merged into IPv6 in 1995.[3]
6	Internet Protocol version 6 (IPv6)[2]	Active.
7	TP/IX The Next Internet (IPv7)[5]	Obsolete.[6]
8	P Internet Protocol (PIP)[7]	Obsolete; merged into SIP in 1993.
9	TCP and UDP over Bigger Addresses (TUBA)	Obsolete.[8]
9	IPv9	April Fools' Day joke.[9]
9	Chinese IPv9	Abandoned.
10–14		Unassigned.
15	Version field sentinel value	Reserved.

History

During the development of the first version of the Internet Protocol in the 1970s, the initial experimental versions 1 to 3 were not standardized. The first working version that was widely deployed was assigned version number 4.[10]

A separate protocol based on reliable connections was developed and assigned version 5.

IP version 7 was chosen in 1988 by R. Ullmann as the next IP version because he incorrectly assumed that version 6 was in use for ST-II. However, ST-II had reused version 5 of the original ST protocol.[5]: 7 

In the early 1990s, when it became apparent that IPv4 could not sustain routing in a growing Internet, several new Internet Protocols were proposed. The Internet Protocol that finally emerged was assigned version number 6, being the lowest free number greater than 4.

The PIP protocol and TUBA protocol used versions 8 and 9, following version 7 for TP/IX.

In 2004, an IPv9 protocol was developed in China using 256-bit addresses.

References

1. J. Postel, ed. (September 1981). INTERNET PROTOCOL - DARPA INTERNET PROGRAM PROTOCOL SPECIFICATION. IETF. doi:10.17487/RFC0791. STD 5. RFC 791. IEN 128, 123, 111, 80, 54, 44, 41, 28, 26. Internet Standard 5. Obsoletes RFC 760. Updated by RFC 1349, 2474 and 6864.
2. S. Deering; R. Hinden (July 2017). Internet Protocol, Version 6 (IPv6) Specification. Internet Engineering Task Force. doi:10.17487/RFC8200. STD 86. RFC 8200. Internet Standard 86. Obsoletes RFC 2460.
3. Jeff Doyle; Jennifer Carroll (2006). Routing TCP/IP. Vol. 1 (2 ed.). Cisco Press. p. 8. ISBN 978-1-58705-202-6.
4. L. Delgrossi; L. Berger, eds. (August 1995). Internet Stream Protocol Version 2 (ST2) Protocol Specification - Version ST2+. Network Working Group. doi:10.17487/RFC1819. RFC 1819. Historic. Obsoletes RFC 1190 and IEN 119.
5. R. Ullmann (June 1993). TP/IX: The Next Internet. Network Working Group. doi:10.17487/RFC1475. RFC 1475. Historic. Obsoleted by RFC 6814.
6. C. Pignataro; F. Gont (November 2012). Formally Deprecating Some IPv4 Options. Internet Engineering Task Force. doi:10.17487/RFC6814. ISSN 2070-1721. RFC 6814. Proposed Standard. Obsoletes RFC 1385, 1393, 1475 and 1770.
7. P. Francis (May 1994). Pip Near-term Architecture. Network Working Group. doi:10.17487/RFC1621. RFC 1621. Historical.
8. Ross Callon (June 1992). TCP and UDP with Bigger Addresses (TUBA), A Simple Proposal for Internet Addressing and Routing. Network Working Group. doi:10.17487/RFC1347. RFC 1347. Historic.
9. J. Onions (1 April 1994). A Historical Perspective On The Usage Of IP Version 9. Network Working Group. doi:10.17487/RFC1606. RFC 1606. Informational. This is an April Fools' Day Request for Comments.
10. J. Postel, ed. (January 1980). INTERNET PROTOCOL - DARPA INTERNET PROGRAM PROTOCOL SPECIFICATION. IETF. doi:10.17487/RFC0760. RFC 760. IEN 128. Obsolete. Obsoleted by RFC 791. Replaces IEN 123, 111, 80, 54, 44, 41, 28 and 26. Updated by RFC 777.