>
> I know this is a bit late but:
>
> Section 5.1's sythesis of MX records based on the presence of
> AAAA records is a bad idea.
>
> If no MX records are found, but an address
> RR (i.e., either an IPv4 A RR or an IPv6 AAAA RR, or their
> successors) is found, the address RR is treated as if it was
> associated with an implicit MX RR, with a preference of 0, pointing
> to that host.
>
> Synthesizing a MX record on NODATA to a MX lookup and a
> subsequent successful AAAA lookup is bad engineering decision.
> It will work reasonably well for IPv4 only + dual stack
> envirionment. It will not work well 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 RRSet 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 target mail domain.
>
> * it changes the definition of what it means to exist in
> the mail domain and you will have different MTA/MSA making
> different existance decisions. Some will say that AAAA +
> no MX exist but others will say that the site does not
> exist.
>
> e.g.
> a new (IPv6 aware) MSA which is configured to relay through
> a old (non-AAAA aware) MTA on its outward bound path.
>
> 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
It should be noted that direct to address for IPv4 or IPv6
addesses is reasonable when there isn't any appropriate
records (MX, A or AAAA) in the DNS and the MTA is configured
to use /etc/host, NIS etc.
Mark
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: [EMAIL PROTECTED]
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