single dns query for A and AAAA

Havard Eidnes he at
Tue Feb 19 08:46:47 CET 2013

> So, i was wondering if anyone has compared the following two
> scenarios in terms of speed, performance and IPv4v6/IPv4
> preference:
> 2 simultaneous dns queries (a & aaaa)
> 1 single dns query (any)
> I'm almost 100% sure that the "any" query will be too heavy for
> many domains (esp with DNSSEC), [...]

That's not the primary issue with that method.  The issue is that
this will simply not work, for other reasons:

For this to work, the client machine would have to ask one of the
authoritative name servers for the zone in which the name you
query for is located.  That's however not normally what you do:
instead, a client machine (which normally just implements a stub
resolver) sends its query to a local recursive resolver, who then
takes it upon himself to find the name servers for the zone to
query.  This recursive resolver has a cache, and if some other
client has already asked the recursive resolver for the "A"
record for the name you want to query with "any" for, you will
get as a response to your "any" query whatever the recursive
resolver has in its cache for the name at that particular point
in time, in this case just the "A" record, even though there may
exist an "AAAA" record (and other records) in the zone served by
the authoritative name servers for the zone.  Such is the nature
of "any" queries.

I'll leave it to somoeone else to follow up on your other
questions / suggestions.


- Håvard

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