On Jul 18, 2014, at 10:18 AM, Tony Finch <d...@dotat.at> wrote:

> Paul Vixie <p...@redbarn.org> wrote:
>> 
>> what's unstated here is that every SMTP sender who encounters such an MX
>> without understanding its new meaning will do two or three lookups: ".
>> MX",
> 
> No, MTAs do not look up MX records for MX targets.
> 
>> [". AAAA",] and ". A".
> 
> But they might do these lookups, yes.
> 
> If this is a worry for the root server operators (but I thought they had
> said in the past that it doesn't pose a problem) then the draft could
> specify a canonical address-less domain lower down the hierarchy, e.g.
> empty.as112.arpa (making use of the AS112 DNAME proposal).
> 
> Tony.
> -

Many years ago Joe Abley and I suggested to create a special name for exactly 
this purpose
a name that was guaranteed to never exist in the DNS thus the first lookup 
would always return NXDOMAIN thus the A+AAAA lookups would never take place. 
http://tools.ietf.org/html/draft-jabley-sink-arpa-03

        Olafur

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