Re: [spfbis] RFC6147 and RFC7208 interoperability issues

[Scott Kitterman <[e-mail]>]

On Monday, February 7, 2022 10:47:13 AM EST John Levine wrote:
> It appears that Scott Kitterman  <[e-mail]> said:
> >Reading RFC 7050, it looks like ipv4only.arpa can return more than one
> >name. That would seem to be a complication if I'm reading it correctly.
> >
> >As a practical matter, it probably doesn't matter, but RFC 7050 doesn't
> >update RFC 6147, so in theory other prefix determination methods could be
> >used.
> >
> >I guess the ::ffff:0:0/96 (IPv4-mapped Address) prefix should be considered
> >similarly.
> >
> >Is there enough here that it would be worth an Applicability Statement?
> 
> On the one hand, I think the implementation would be quite easy.  When the
> SPF library receives an external IPv6 address to check, it does the
> ipv4only lookup and if the prefix on the address is one of the mapped ones,
> it rewrites the IPv6 address to the corresponding IPv4 address and passes
> it along to the rest of the SPF code.
> 
> On the other hand, since this is the first time in fifteen years that anyone
> has run into this, I don't think it's worth fixing.  If you want to put a
> mail server behind DNS64, you're on your own.

I think that's a fair reading of RFC 6147 itself:

> 6.  Deployment Notes
>
> While DNS64 is intended to be part of a strategy for aiding IPv6
> deployment in an internetworking environment with some IPv4-only and
> IPv6-only networks, it is important to realize that it is
> incompatible with some things that may be deployed in an IPv4-only or
> dual-stack context.

OTOH, how long has DNS64 been deployed (I don't know)?  Will it see increased 
deployment in the future, so this is the leading edge of the issue?

Personally, I don't have an interest in DNS64, but I think it's not 
unreasonable for the IETF to document how to navigate the intersection of two 
standards track documents.

Scott K