Editing Internet Protocol (section)

== Version history ==
[[File:TCP and IP protocols development timeline-en.svg|thumb|right|A timeline for the development of the transmission control Protocol TCP and Internet Protocol IP]]
[[File:First Internet Demonstration, 1977.jpg|thumb|right|First Internet demonstration, linking the [[ARPANET]], [[PRNET]], and [[SATNET]] on November 22, 1977]]
In May 1974, the [[Institute of Electrical and Electronics Engineers]] (IEEE) published a paper entitled "A Protocol for Packet Network Intercommunication".<ref>{{Cite journal|last1=Cerf|first1=V.|last2=Kahn|first2=R.|date=1974|title=A Protocol for Packet Network Intercommunication|url=https://www.cs.princeton.edu/courses/archive/fall06/cos561/papers/cerf74.pdf|journal=IEEE Transactions on Communications|volume=22|issue=5|pages=637–648|doi=10.1109/TCOM.1974.1092259|issn=1558-0857|quote=The authors wish to thank a number of colleagues for helpful comments during early discussions of international network protocols, especially R. Metcalfe, R. Scantlebury, D. Walden, and H. Zimmerman; D. Davies and L. Pouzin who constructively commented on the fragmentation and accounting issues; and S. Crocker who commented on the creation and destruction of associations.|access-date=2020-04-06|archive-date=2017-01-06|archive-url=https://web.archive.org/web/20170106204542/http://www.cs.princeton.edu/courses/archive/fall06/cos561/papers/cerf74.pdf|url-status=live}}</ref> The paper's authors, [[Vint Cerf]] and [[Bob Kahn]], described an [[internetworking]] protocol for sharing resources using [[packet switching]] among [[network node]]s. A central control component of this model was the Transmission Control Program that incorporated both connection-oriented links and datagram services between hosts. The monolithic Transmission Control Program was later divided into a modular architecture consisting of the [[Transmission Control Protocol]] and [[User Datagram Protocol]] at the [[transport layer]] and the Internet Protocol at the [[internet layer]]. The model became known as the ''Department of Defense (DoD) Internet Model'' and ''[[Internet protocol suite]]'', and informally as ''TCP/IP''.

The following [[Internet Experiment Note]] (IEN) documents describe the evolution of the Internet Protocol into the modern version of IPv4:<ref>{{Cite web |title=Internet Experiment Note Index |url=https://www.rfc-editor.org/ien/ien-index.html |access-date=2024-01-21 |website=www.rfc-editor.org}}</ref>
* [http://www.rfc-editor.org/ien/ien2.txt IEN 2] ''Comments on Internet Protocol and TCP (''August 1977) describes the need to separate the TCP and Internet Protocol functionalities (which were previously combined).  It proposes the first version of the IP header, using 0 for the version field.
* [http://www.rfc-editor.org/ien/ien26.pdf IEN 26] ''A Proposed New Internet Header Format (''February 1978) describes a version of the IP header that uses a 1-bit version field.
* [http://www.rfc-editor.org/ien/ien28.pdf IEN 28] ''Draft Internetwork Protocol Description Version 2 (''February 1978) describes IPv2.
* [http://www.rfc-editor.org/ien/ien41.pdf IEN 41] ''Internetwork Protocol Specification Version 4 (''June 1978) describes the first protocol to be called IPv4.  The IP header is different from the modern IPv4 header.
* [http://www.rfc-editor.org/ien/ien44.pdf IEN 44] ''Latest Header Formats (''June 1978) describes another version of IPv4, also with a header different from the modern IPv4 header.
* [http://www.rfc-editor.org/ien/ien54.pdf IEN 54] ''Internetwork Protocol Specification Version 4 (''September 1978) is the first description of IPv4 using the header that would become standardized in 1980 as {{IETF RFC|760}}.
* IEN 80
* IEN 111
* IEN 123
* IEN 128/RFC 760 (1980)

IP versions 1 to 3 were experimental versions, designed between 1973 and 1978.<ref name="Coty">{{cite web |author=Stephen Coty |date=2011-02-11 |title=Where is IPv1, 2, 3, and 5? |url=https://blog.alertlogic.com/blog/where-is-ipv1,-2,-3,and-5/ |url-status=dead |archive-url=https://web.archive.org/web/20200802011845/https://blog.alertlogic.com/blog/where-is-ipv1,-2,-3,and-5/ |archive-date=2020-08-02 |access-date=2020-03-25}}</ref> Versions 2 and 3 supported variable-length addresses ranging between 1 and 16 octets (between 8 and 128 bits).<ref>{{cite IETF |last1=Postel |first1=Jonathan B. |date=February 1978 |title=Draft Internetwork Protocol Specification Version 2 |ien=28 |autolink=no |url=https://www.rfc-editor.org/ien/ien28.pdf |website=RFC Editor |access-date=6 October 2022 }} {{Webarchive|url=https://web.archive.org/web/20190516090051/https://www.rfc-editor.org/ien/ien28.pdf |date=16 May 2019 }}</ref> An early draft of version 4 supported variable-length addresses of up to 256 octets (up to 2048 bits)<ref>{{cite IETF |last1=Postel |first1=Jonathan B. |date=June 1978 |title=Internetwork Protocol Specification Version 4 |ien=41 |autolink=no |url=https://www.rfc-editor.org/ien/ien41.pdf |website=RFC Editor |access-date=11 February 2024 }} {{Webarchive|url=https://web.archive.org/web/20190516090053/http://www.rfc-editor.org/ien/ien41.pdf |date=16 May 2019 }}</ref> but this was later abandoned in favor of a fixed-size 32-bit address in the final version of [[IPv4]]. This remains the dominant internetworking protocol in use in the [[Internet Layer]]; the number 4 identifies the protocol version, carried in every IP datagram. IPv4 is defined in {{IETF RFC|791}} (1981).

Version number 5 was used by the [[Internet Stream Protocol]], an experimental streaming protocol that was not adopted.<ref name="Coty"/>

The successor to IPv4 is [[IPv6]]. IPv6 was a result of several years of experimentation and dialog during which various protocol models were proposed, such as TP/IX ({{IETF RFC|1475}}), PIP ({{IETF RFC|1621}}) and TUBA (TCP and UDP with Bigger Addresses, {{IETF RFC|1347}}). Its most prominent difference from version 4 is the size of the addresses. While IPv4 uses [[32 bits]] for addressing, yielding c. 4.3 [[1,000,000,000 (number)|billion]] ({{val|4.3|e=9}}) addresses, IPv6 uses [[128-bit]] addresses providing c. {{val|3.4|e=38}} addresses. Although adoption of IPv6 has been slow, {{as of|2023|01|lc=yes}}, most countries in the world show significant adoption of IPv6,<ref>{{Cite web|title=IPv6 Adoption in 2021|url=https://labs.ripe.net/author/stephen_strowes/ipv6-adoption-in-2021/|first1=Stephen|last1=Strowes|date=4 Jun 2021|access-date=2021-09-20|website=RIPE Labs|language=en-US|archive-date=2021-09-20|archive-url=https://web.archive.org/web/20210920213008/https://labs.ripe.net/author/stephen_strowes/ipv6-adoption-in-2021/|url-status=live}}</ref> with over 41% of Google's traffic being carried over IPv6 connections.<ref>{{Cite web |title=IPv6 |url=https://www.google.com/intl/en/ipv6/statistics.html#tab=ipv6-adoption |access-date=2023-05-19 |website=Google |archive-date=2020-07-14 |archive-url=https://web.archive.org/web/20200714184705/https://www.google.com/intl/en/ipv6/statistics.html#tab=ipv6-adoption |url-status=live }}</ref>

The assignment of the new protocol as IPv6 was uncertain until due diligence assured that IPv6 had not been used previously.<ref>{{cite web|last1=Mulligan|first1=Geoff|title=It was almost IPv7|url=http://archive.oreilly.com/cs/user/view/cs_msg/25036|website=O'Reilly |access-date=4 July 2015|archive-url=https://web.archive.org/web/20150705060055/http://archive.oreilly.com/cs/user/view/cs_msg/25036|archive-date=5 July 2015|url-status=dead}}</ref> Other Internet Layer protocols have been assigned version numbers,<ref>{{Cite web|url=https://www.iana.org/assignments/version-numbers/version-numbers.xhtml|title=IP Version Numbers|website=Internet Assigned Numbers Authority|access-date=2019-07-25|archive-date=2019-01-18|archive-url=https://web.archive.org/web/20190118144623/https://www.iana.org/assignments/version-numbers/version-numbers.xhtml|url-status=live}}</ref> such as 7 (''IP/TX''), 8 and 9 (''historic''). Notably, on April 1, 1994, the [[IETF]] published an [[April Fools' Day RfC]] about IPv9.<ref>{{IETF RFC|1606}}: ''A Historical Perspective On The Usage Of IP Version 9''. April 1, 1994.</ref> IPv9 was also used in an alternate proposed address space expansion called TUBA.<ref>{{cite IETF |rfc=1347 |title=TCP and UDP with Bigger Addresses (TUBA), A Simple Proposal for Internet Addressing and Routing |author=Ross Callon |date=June 1992}}</ref> A 2004 Chinese proposal for [[IPv9 (China)|an IPv9 protocol]] appears to be unrelated to all of these, and is not endorsed by the IETF.

===IP version numbers===
As the version number is carried in a 4-bit field, only numbers 0–15 can be assigned.
{| class="wikitable"
|-
!IP version
!Description
!Year
!Status
|-
!0
|Internet Protocol, pre-v4||N/A||Reserved<ref name="routing tcp/ip">{{Cite book|title=Routing TCP/IP|volume=1|edition=2|author1=Jeff Doyle|author2=Jennifer Carroll|year=2006|isbn=978-1-58705-202-6|publisher=Cisco Press|page=8}}</ref>
|-
!1
|Experimental version||1973||Obsolete
|-
!2
|Experimental version||1977||Obsolete
|-
!3
|Experimental version||1978||Obsolete
|-
!4
|[[Internet Protocol version 4]] (IPv4){{Ref RFC|791|repeat=yes}}||1981||Active
|-
!rowspan=3|5
|[[Internet Stream Protocol]] (ST)||1979||Obsolete; superseded by ST-II or ST2
|-
|[[Internet Stream Protocol]] (ST-II or ST2){{Ref RFC|1819}}||1987||Obsolete; superseded by ST2+
|-
|[[Internet Stream Protocol]] (ST2+)||1995||Obsolete
|-
!rowspan=2|6
|Simple Internet Protocol (SIP)||N/A||Obsolete; merged into IPv6 in 1995<ref name="routing tcp/ip" />
|-
|[[Internet Protocol version 6]] (IPv6){{Ref RFC|8200|repeat=yes}}||1995||Active
|-
!7
|TP/IX The Next Internet (IPv7){{Ref RFC|1475}}||1993||Obsolete{{Ref RFC|6814}}
|-
!8
|P Internet Protocol (PIP){{Ref RFC|1621}}||1994||Obsolete; merged into SIP in 1993
|-
!rowspan=3|9
|TCP and UDP over Bigger Addresses (TUBA)||1992||Obsolete{{Ref RFC|1347}}
|-
|IPv9||1994||[[April Fools' Day]] joke{{Ref RFC|1606}}
|-
|[[Chinese IPv9]]||2004||Abandoned
|-
!10–14
|N/A||N/A||Unassigned
|-
!15
|''Version field sentinel value''||N/A||Reserved
|}