any requests

[Tony Finch]

Vernon Schryver <vjs at rhyolite.com> wrote:
>
> > [ANY query for combined MX/A lookup was] a bad hack then and it
> > has remained a bad hack :-)
>
> I would not agree if you could rely on the open resolvers continuing
> to do what they're doing, if you didn't care about parsing 3 or 4
> KBytes of irrelevant bits to get the RRsets you want, and if you don't
> care about spending 9 or 10 IP packets on a truncated UDP responce and
> then a full TCP response instead of 6 on 3 separate queries.
>
> With BIND as your DNS server, it could be a win for bursts of mail to
> a single SMTP server if your SMTP client is too dumb to do the obvious,
> safe caching.  At worst you would need to ask for ANY, MX, A, and AAAA,
> but some of the time the ANY would have all of the RRsets.

There are other caveats:

The ANY query does not trigger additional section processing, so if you
find MX records in the result you have to make follow-up queries to get
the A and AAAA records of the targets; if you made an MX query in the
first place you often don't need to make more queries.

The ANY query does not trigger alias processing, so if there is a CNAME
chain you have to follow it yourself. This is a waste because if you made
an MX query in the first place the server would have given you the whole
chain without further queries.

Tony.
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