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Re: current usage of AAAA implicit MX?

2008-04-05 13:45:04
On 2008-04-05 22:03:17 +0200, Arnt Gulbrandsen wrote:
Peter J. Holzer writes:
On 2008-04-04 17:30:29 -0400, Robert A. Rosenberg wrote:
RFC 3974
It, BTW, REQUIRES an MX if there are any IPv6 MTAs  and only supports 
A-Fallback in the absence of an MX


"For the transition period, all mail domains should have MX records such 
that MX targets with IPv4 and IPv6 addresses exist"?

That doesn't say anything specifically the fallback. The fallback is
clearly specified in section 3 and includes fallback to an AAAA record.
So it is false that RFC 3974 "only supports A-Fallback in the absence of
an MX".

It also states that in the presence of an MX containing IPv6 address
references, an IPv4-Only stack should ignore the IPv6 addresses

Yes, of course. It cannot reach them anyway. Just as IPv6-only hosts 
can ignore A records since they cannot reach them either.

An IPv6-only host must use the presence/absence of A records to generate 
the DSN. The DSN status code is 5.1.2 if there's no A and 5.4.x if 
there is an A but no way to reach it (ie. no configured relay).

Hmm. That would (after substituting AAAA for A) also apply to an IPv4
host, but it is unreasonable to expect that. I'd file that under
"quality of implementation".

In any case that's not in RFC 3974.


   _  | Peter J. Holzer    | It took a genius to create [TeX],
|_|_) | Sysadmin WSR       | and it takes a genius to maintain it.
| |   | hjp(_at_)hjp(_dot_)at         | That's not engineering, that's art.
__/   | |    -- David Kastrup in comp.text.tex

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