On 2012-02-14 13:32, Dave CROCKER wrote:
>
>
> On 2/13/2012 4:17 PM, Brian E Carpenter wrote:
>> People say this from time to time, but it's a complete myth.
>
> well, not completely...
>
>
>> IPv4 provides no mechanism whatever for addresses greater than 32 bits.
>> Therefore, mathematically, there is no possible design for an IP with
>> bigger addresses that is transparently backwards compatible. We've known
>> that since at least 1992.
>
>
> The path that the IETF followed ensured the maximum amount of
> incompatibility. Really a completely independent stack.
>
> In contrast, the IETF could easily have chose a path toward minimizing
> incompatibility that would have allowed IPv6 to interwork with IPv4,
> within the limitations of the v4 address space.
>
> That is, the IETF could begun IPv6 by assigning to it IPv4 addresses,
> reserving the remainder for latter definition and allocation. It could
> have targeted simple, basic reformatting at the IP level to permit early
> IPv6 adoption to require a minimal gateway for interworking with the
> IPv4 world.
There were very specific reasons why this was not done. And it doesn't
change the fact that an old-IP-only host cannot talk to a new-IP-only host
without a translator. It is that fact that causes our difficulties today.
Brian
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