> On Tue, 15 Jan 2008, Mark Andrews wrote:
> >
> > Since there is no [MX] fallback to AAAA
>
> Wrong. http://www1.ietf.org/mail-archive/web/ietf/current/msg49841.html
>
> Tony.
Since when has Informational been equivalent to Standard?
Synthesizing a MX record on NODATA to a MX lookup or a
subsequent AAAA lookup is bad engineering decision. It
will work reasonably well for IPv4 only + dual stack
envirionment. It will not work will for IPv4 only + dual
stack + IPv6 only envirionment.
The reason it is a bad engineering decision is that:
* the IPv4 only world needs a MX to find a dual stack MTA to
relay into the IPv6 network.
* the IPv6 world has a raft of solutions which will allow it
to initiate a connection to a IPv4 only MTA without having
to find a dual stack MX for the mail domain.
* it changes the definition of what it means to exist in
the mail domain and you will have different MTA's making
different existance decisions. Some will say that AAAA +
no MX exist but others will say that the site does not
exist.
Do you really thing we should be trying to force a upgrade
of all MTA's on the planet to support MX synthesis from
AAAA when there is no engineering need to to this?
MX from A was a transition strategy. IPv6 only sites have a
transition strategy that doesn't require synthesis. It is
advertise a dual stack MX. At some point in the future sites
will stop having a dual stack MX, the same way they stopped
adding A records for mail only domains back in the 90's.
Mark
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: [EMAIL PROTECTED]
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