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Re: IPv6<->IPv4 address translation is not NAT?
On 2007-12-08 13:38, Geoff Huston wrote:
Ralph Droms wrote:
Geoff - in the v6ops meeting you said that the IPv6 transition problem
is not a NAT problem. Can you explain in more detail? There must be,
I think. a translation between addresses from incompatible address
spaces, just like NATv4. What do you think is the difference?
The point I was trying to make is that NATs are not "just" Network
Address Translators - they are in fact used for a particular style of
Network address translation which is asymmetric. We all know how a NAT
is defined - it has an "inside" and an "outside" and packets from the
"inside" that are heading to the "outside have one set of transforms
applied to the IP source field and packets in tyhe opposite direction
have a comparable set of transforms applied to the IP destination field.
So we have assumptions of "inside" and "outside", and only one part of
the header is touched, etc etc.
The point I was making at the microphone in the WG was that the V4 / V6
translation problem shares very little with the asymmetric NATS that we
know as "NAT" as this protocol transform is an entirely different form
of address translation which has different triggers, semantics and
states. And I was trying to say that calling them both "NATS" is
uncomfortable for me.
Now is that clearer or muddier?
I think an important point of commonality is that when translating
between a smaller and a larger address space, you're forced to
deal with port mapping as well as with address translation.
That is the same problem whether the smaller/larger pair
is single-IPv4/RFC1918 or IPv4/IPv6.
Maybe we should talk about address sharing rather than address
translation?
Brian