Subject: Old / new NAT-PT coexistance?

From: Iljitsch van Beijnum <[email-masked]>
Date: Wed, 30 Jan 2008 19:13:45 +0100

Question for the WG:

Do we care about coexistance of old style and new style NAT-PT?

The new style that Brian and I are working on is going to require  
changes on the IPv6 side, which won't be made over night: looking up A  
records by the hosts themselves rather than having a DNS ALG generate  
synthetic AAAA records for IPv4-only destinations.

The problem is that you would have to provision different DNS  
resolvers for hosts that are IPv6-only and do not support the new  
style NAT-PT versus the ones that do and dual stack hosts. This could  
be a problem. Solution: have hosts that do DNS lookups over IPv6  
transport indicate that they support new style NAT-PT and don't need  
the synthetic AAAA records through EDNS0.

Is this something we want or can we assume that old style NAT-PT is  
dead so we don't have to consider issues relating to it?

---

From: Fred Baker <[email-masked]>
Date: Wed, 30 Jan 2008 10:32:06 -0800

Speaking strictly for myself, I don't see any reason to believe that  
NAT-PT is dead. I believe that v6ops doesn't like it, but it is  
implemented and in use. We all know how folks who are successfully  
using something automatically turn it off and use something else when  
we tell them to...

On Jan 30, 2008, at 10:13 AM, Iljitsch van Beijnum wrote:

> changes on the IPv6 side, which won't be made over night: looking  
> up A records by the hosts themselves rather than having a DNS ALG  
> generate synthetic AAAA records for IPv4-only destinations.
>
> style NAT-PT versus the ones that do and dual stack hosts. This  
> could be a problem. Solution: have hosts that do DNS lookups over  
> IPv6 transport indicate that they support new style NAT-PT and  
> don't need the synthetic AAAA records through EDNS0.
>

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Wed, 30 Jan 2008 20:18:49 +0100

On 30-jan-2008, at 19:32, Fred Baker <[email-masked]> wrote:

> using something automatically turn it off and use something else  
> when we tell them to...
>>
>>
>>
>>

So that would be a "yes" to the EDNS0 idea?

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Thu, 31 Jan 2008 12:25:45 +0100

On 30 jan 2008, at 19:13, Iljitsch van Beijnum wrote:

> changes on the IPv6 side, which won't be made over night: looking up  
> A records by the hosts themselves rather than having a DNS ALG  

> IPv6 transport indicate that they support new style NAT-PT and don't  
> need the synthetic AAAA records through EDNS0.

Another option would be for the server to simply always generate the  
synthetic AAAA records as per existing NAT-PT, but then add an EDNS0  
option that identifies the synthetic addresses. Hosts that are aware  
of this then know they're really talking to IPv4 destinations and  
could present ::ffff:x.x.x.x addresses (or x.x.x.x addresses) to  
applications so applications can adjust their behavior to what's  
needed for IPv4 operation.

This also nicely avoids the whole issue of how to configure/discover  
the /96 prefix used by the translator. The downside is that there will  
be significant old style NAT-PT and there is still the chance of  
leakage of the synthetic AAAA records as long as DNS servers don't  
implement the new EDNS0 option and filter out these records.

Thoughts?