NAT v6->v4 and v4->v6 (was Re: WG Action: Conclusion of IP Version 6 )

Durand, Alain Alain_Durand at
Fri Sep 28 12:45:58 UTC 2007

The IETF thinking for the last 10+ years (and I include myself in this) had been that dual stack was the answer and most things would be converted to dual stack before we ran out of v4.

Well, it has not happen.

There is still very little v6 deployment and we will be running out of v4 space soon (instantiate soon by your particular prediction of the day you won't be able to get space from your RIR, either because there is no more or because you do not qualify any longer).

Given the above, it is clear that we are gong to see devices (which might be dual stack *capable*) that will be deployed and provisionned with *v6-only*...

At the edge of the network, where we have devices by the millions and where address space is a critical issue and dual-stack is a non starter, this is already under way...

It is also becoming apparent that:

- the "core internet" (ie the web and any infrastructure server) will take a long time to move to v6 and/or dual stack.

- new v6-only edges will have to communicate with it. So we need v6->v4 translation in the core

- legacy v4 PCs (think win95 up to win XP) using RFC1918 addresses behind a home gateway  will never be able to upgrade to an IPv6-only environment. So if we provision the home gateway with v6-only (because there will be a point where we do not have any global v4 addresses left for it) those legacy PCs are going to need a double translation, v4->v6 in the home gateway and then v6 back to v4 in the core. Note: a double private v4->private v4->global v4 translation would work too, but if you are running out of private space as well, this is also a non-starter...

- there are a number of internal deployment cases where net 10 is just not big enough, thus the idea to use v6 to glue several instances of private space together as a 'super net 10'. For this to work, legacy devices that cannot upgrade to v6 need to go through a translation v4->v6.

So, no, NAT v4->v6 or v6-v4 does not solve world hunger but solve very real operational problems.

    - Alain.

----- Original Message -----
From: Jari Arkko <jari.arkko at>
To: Durand, Alain
Cc: Randy Bush <randy at>; nanog at <nanog at>
Sent: Fri Sep 28 00:25:11 2007
Subject: Re: WG Action: Conclusion of IP Version 6 (ipv6)

Randy, Alain,

>     o nat-pt with standardized algs for at least dns, smtp, http, sip, and
>     rtp
> -->> This is on my top 3 hot topics. And make it works both way, v4 to
> v6 and v6 to v4.
> And also don’t call it NAT-PT. That name is dead.

For what it is worth, this is one of the things that I want
to do. I don't want to give you an impression that NAT-PT++
will solve all the IPv6 transition issues; I suspect dual stack
is a better answer. But nevertheless, the IETF needs to
produce a revised spec for the translation case. Fred and
I are organizing an effort to do this.


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