[dns-operations] extra records in resolver answer, any benefit?

Florian Weimer fw at deneb.enyo.de
Tue Jan 27 16:00:58 UTC 2015

* Tony Finch:

> bert hubert <bert.hubert at netherlabs.nl> wrote:
>> It is all optional, and nobody does anything with that data. In fact stub
>> resolvers do very little with what they receive. So for example, even the
>> additional processing for an MX record is completely ignored mostly.
> Yes.
> The difficulty with MX (and SRV) additional data is that you don't get a
> clear indication whether the target address records are nonexistent or
> just unavailable, so it tends to be easier to look them up regardless of
> the contents of the additional section.

Exactly.  Exim tried to do the optimization, but did not cover a
corner case, and we had very obscure intermittent mail delivery
failures as a result.  Not nice.

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