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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