Whatever happened to IPv5?

In response to a recent question asking what happened to IPv5, I offer the following response.

The Internet Assigned Numbers Authority (IANA) maintains a centralized repository of Internet Protocol parameters. This function is critical to assure uniqueness of parameter settings to keep the Internet Protocol operating smoothly and without ambiguity.

Among the parameters maintained by IANA are the assigned values of the version field of the IP header. As you might guess, for IPv4, the version value is 4, and for IPv6, the value is 6. But as new protocols are developed within the Internet community, parameter value assignments are requested of and assigned by IANA. In the case of the IP version parameter, the value of 5 has been assigned to the Internet Stream Protocol an experimental real-time streaming protocol.


In fact, the IP version parameter has not only been assigned values 4, 5 and 6, it has also been assigned values of 7, 8 and 9 as shown in the following table from IANA:

DecimalKeywordVersionReference
0-1ReservedRFC4928
2-3Unassigned
4IPInternet ProtocolRFC791
5STST Datagram ModeRFC1190
6IPv6Internet Protocol version 6RFC1752
7TP/IXTP/IX: The Next InternetRFC1475
8PIPThe P Internet ProtocolRFC1621
9TUBATUBARFC1347
10-14Unassigned
15Reserved

If the next version of IP beyond IPv6 was defined as of today, it would be known as IPv10! But hopefully with plentiful IPv6 address space, we won’t need to go there at least in the next 40 years!

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