Duplicating queries??

Barry Margolin barmar at alum.mit.edu
Sun Feb 21 04:51:49 UTC 2010


In article <mailman.494.1266688491.21153.bind-users at lists.isc.org>,
 Daniel Morgan <daniel.morgan at riotm.co.uk> wrote:

> On Sat, 2010-02-20 at 11:38 -0500, Barry Margolin wrote:
> > In article <mailman.486.1266649694.21153.bind-users at lists.isc.org>,
> >  Daniel Morgan <daniel.morgan at riotm.co.uk> wrote:
> > 
> > > I have a couple of BIND servers that I have inherited.  I'm getting some
> > > upstream  complaints that one of them is issuing duplicate queries on
> > > occasions - probably about a dozen times a day. When it happens, sure
> > > enough I find this in the logs: 
> > > 
> > > named[6905]: 18-Feb-2010 22:31:41.201 client 82.70.24.23#55710: query:
> > > 28.214.138.70.itx.munged.org.uk IN TXT + 
> > > named[6905]: 18-Feb-2010 22:31:42.560 client 82.70.24.23#52806: query:
> > > 28.214.138.70.itx.munged.org.uk IN TXT + 
> > > 
> > > Here the last query is identical to the first buy made just over a
> > > second later.
> > > 
> > > I'm not sure this is an issue with BIND and I suspect that it may be the
> > > program (Postfix) that is querying the server firing off occasional
> > > duplicate queries? I'm clutching at straws to understand what is going
> > > on here - can anyone offer me some advice?
> > 
> > Did it get a response to the first query?  If not, the second one is 
> > simply retrying because it timed out waiting for a response.
> > 
> You know something, that had not crossed my mind. I can't think of any
> easy way to check this - but looking though all the other logs on the
> system - right down to the wan link, nothing is out of place.

I just realized that the log you showed above is the log of queries your 
server received, not what it sent.  There's nothing unusual with a 
client repeating queries to its resolver, since clients generally don't 
cache the results.  The server should answer the second query from its 
cache.

You could turn on debug logging in BIND, or use a packet capture program 
to watch DNS traffic between your server and the one that's complaining.

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
*** PLEASE don't copy me on replies, I'll read them in the group ***



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