Performance Tuning RHEL 5 and Bind

Steven Carr sjcarr at
Sun Oct 20 06:33:29 UTC 2013

On 20 October 2013 02:34, brett smith <brett.s9999 at> wrote:
> When all the Windows PC's are switched to our resolver, bind stops responding.
> rndc querylog shows queries coming thru, I changed  tcp-clients from
> 1000 to 10000 but DNS seems lagging, so we switched back to the
> original Windows Domain resolver. Besides increasing open files
> tuning, what TCP / sysctl or named.conf settings can be set to
> optimize / speed up DNS queries? Because it seems that Windows clients
> use TCP instead of UDP when looking at netstat on the server.

It will depend on the type and size of the query (and on the
configuration/structure of the network in-between) as to whether
Windows uses UDP or is forced to switch to TCP.

But the option you are probably looking for is "recursive-clients" and
then pick a number. The default is 1000, so this is probably why if
all of your systems are querying at once it stops responding to some
of them.

Other than that it's a case of how much memory, CPU. Is it a VM? if so
have you reserved enough resources for it? What data is it serving?
caching only? authoritative for any zones? Is query logging enabled?
(this is a big performance hit as it has to write everything to disk,
so your disk is going to be a bottleneck).

Tuning is not something that you can be told "this is what to do",
there are a huge number of factors that will influence which
parameters to tweak. But I'd definitely look to the
"recursive-clients" option for starters.


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