NIST IPv6 document
owen at delong.com
Sat Jan 8 23:03:43 CST 2011
> If you define a new protocol version as one that means devices with
> older protocol generations of firmware/software may not interoperate
> reliably with devices with new protocol generations of
> firmware/software, then IPv4 as we know it today is probably at least
> "IPv7" - address classes was a generational change requiring
> software/firmware updates (compare addressing in rfc760 verses rfc791),
> as was classful+subnets and then CIDR.
I think it's defined, instead, in terms of incompatible changes to the
content of the packet header.
More information about the NANOG