odd dns behavior on osx

Bjørn Mork bjorn at mork.no
Sat Jun 19 11:47:31 CEST 2010

Tore Anderson <tore.anderson at redpill-linpro.com> writes:
> * Alan Batie
>> I've been using www.v6.facebook.com since I found out about it earlier
>> this week, and OSX is exhibiting some odd behavior: after a short time
>> (the cache timeout period?), gui apps, specifically firefox and safari
>> complain "can't find host".  From a terminal window, I can ping6 the
>> site, after which firefox and safari can again find it themselves.  Very
>> odd...
> You're experiencing a known OS X bug.  It will send out the A and AAAA
> queries in parallel, and will use the first answer it gets back and
> ignore the second one.  You probably get an NXDOMAIN response to your A
> request first, and therefore the AAAA response you're actually
> interested in gets ignored.

I believe you meant NODATA instead of NXDOMAIN here?

If you send two queries for the same name and one of them returns
NXDOMAIN and the other not, then something is fundamentally broken.  And
it's not the resolver...  But I assume that is not the case you are
talking about.

See RFC2308 for a useful classification of the different negative DNS
results you may encounter.


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