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Re: Modified IPv6 to unmodified IPv4

On 20-okt-2007, at 21:11, Brian E Carpenter wrote:
So that means NAT. What if we can keep the NAT in IPv4 rather than IPv6? So instead of applications talking IPv6 and then having a gateway translate and NAT, we have the applications talk IPv4, carry the IPv4 over IPv6 and then NAT. The interesting part here is that if we integrate the NAT and the translation, we can skip the whole IPv4 provisioning, because the NATed IPv4 address is of no importance to anyone except the application behind the NAT. 


That doesn't cover us for the day when we have true IPv6-only apps
with no reptilian memory of IPv4. I think I'd rather avoid the
application having any knowledge of IPv4 at all. If we're going to
do this horrible thing, let's do it 100%.


Well, the way I see it there are four permutations:

1. both the IPv4 and IPv6 ends are unaware of the translation
2. the IPv4 end is aware of the translation, the IPv6 end isn't
3. the IPv4 end isn't aware of the translation, the IPv6 end is
4. both ends are aware of the translation
The first case, in the form of NAT-PT has fallen into disfavor within the IETF for a variety of reasons, my favorite being that it imports NAT issues into IPv6. Personally, I believe that there is no way to resurrect a type 1. approach that doesn't have much the same issues, but I'd be happy to be proven wrong.
If 1. is out this basically leaves either modifying IPv4 hosts so they can talk to unmodified IPv6 hosts, or modifying IPv6 hosts so they can talk to unmodified IPv4 hosts. The former has the advantage that it keeps IPv6 clean, the latter is more pragmatic because a good part of the IPv4 installed base is presumably unupgradable.
Alternatively, we could go for 4. (or rather, 2. + 3.) and come up with something where one end is modified and the other isn't, and let the operators figure out if and where they want to place the burden of extra protocol layers to talk to the other protocol.
It would be good if the wg could decide on which direction is best, so that we can start work in that direction.