Access to the IPv4 net for IPv6-only systems, was: Re: WG Action: Conclusion of IP Version 6 (ipv6)

Iljitsch van Beijnum iljitsch at
Sun Sep 30 19:30:50 UTC 2007

On 30-sep-2007, at 5:10, John Curran wrote:

> The irony is that the I* rationale for moving NAT-PT to historic
> was "to restore the end-to-end transparency of the Internet"
> and yet the only real chance we have to restore end-to-end
> transparency is to first have a transition to the IPv6 (using
> dual-stack, NAT-PT, and every other tool at our disposal) and
> then over time let present IPv4 destination sites add IPv6 for
> end-to-end transparency based on their actual need for it.
> Instead, central planning may have effectively killed the very
> tool that's needed to allow providers to provision new Internet
> customers over a pure IPv6-only model, and create the right
> motivation for existing Internet sites to go dual-stack and
> actually gain "end to end transparency" via IPv6.

In my opinion, the mistake the IETF made was to "deprecate" NAT-PT  
without coming up with an alternative first.

Originally, my thinking was "sure, NAT-PT doesn't work with  
everything unless you have ALGs for a good number of protocols, but  
it gives you 80% of what you need so it's a good start". But I've  
come to see how having IPv6 applications expect end-to-end IPv6  
connectivity and then have that rug pulled from under them will  
inevitably lead to the same lack of end-to-end transparency in IPv6  
that we currently have with IPv4. And once that can is open, it's  
unlikely we can get the worms to crawl back inside later.

But proxying can be that 80% solution and tunneling IPv4 over IPv6  
can be a 100% solution so we don't have to raise NAT-PT from the dead.

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