On Fri, Feb 06, 2009 at 09:11:43AM -0800, Roderick A. Anderson wrote:
>> mx.trendargentina.com.ar. 0 IN A 10.0.0.208
>> mx.trendargentina.com.ar. 0 IN A 10.0.0.207
>
> What this says to me is every time Postfix requests the MX for
> trendargentina.com.ar the name server software will look it up and come
> back with _either_ 10.0.0.208 or 10.0.0.207 and depending on how many
> other DNS requests are made it might be the same over and over.
No, this is wrong. Postfix shuffles MX host A records of equal priority.
> If your zone file had
>
> trendargentina.com.ar. 0 IN MX 10 mx1.trendargentina.com.ar.
> trendargentina.com.ar. 0 IN MX 10 mx2.trendargentina.com.ar.
>
> ...
>
> mx1.trendargentina.com.ar. 0 IN A 10.0.0.208
> mx2.trendargentina.com.ar. 0 IN A 10.0.0.207
>
>
> Then when Postfix asked for the MX record for trendargentina.com.ar the DNS
> server would send back the two IP addresses and Postfix would
> round-robin/randomize them.
This is wrong, see above.
> I got the DNS info from readings in "Pro DNS and bind" and the Postfix from
> this list and the online documentation.
>
> You implementation has DNS doing the round-robin with the results depending
> on how busy the name server is. Mine lets Postfix do it with a single
> query to the name server.
>
Postfix does not rely on DNS servers shuffling the MX or A RRsets.
--
Viktor.
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