IPv4, 5, 6...

The exhaustion of the central pool of IPv4 addresses is imminent. Exhaustion has led to a resurgence of the simple question ‘what happened ip IPv5?’ and, less commonly, ‘what happened to IPv{0,1,2,3}?’. IANA naturally governs the allocation of IP version numbers, and indeed have a list of all ten of them. The list is as follows:

Certainly the last 4 in this list were designed in response to the IPng white paper solicitation. Jon Postel, for the sake of fairness, applied a version number for each of the candidates, and ultimately IPv6 was chosen.

Regarding IPv{2,3}, the (very informative) internet history mailing list provides an answer: This mailing list post from Vint states that TCP and IP were split sometime around TCPv3, presumably leading to IP packets with version number 3. The suggestion is that there was no IPv2 as we would recognise it.

IPv{0,1} were ever presumably also never used. And just as development of TCP/IP doesn’t map well onto early internet protocol versions, the ‘missing’ versions also don’t map onto NCP, which TCP/IP replaced in early 1983; the packet headers, and indeed the network design and semantics as specified in BBN Report 1822, are very different to what we have today.

Anyway, we squeezed 28 years and 1 month out of IPv4. We’re all well into our IPv6 transition, right?


Posted by Stephen Strowes on Saturday, January 29th, 2011. You can follow me on twitter.

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