High recursive client counts

Eliezer Croitoru eliezer at ngtech.co.il
Wed Mar 26 20:23:22 UTC 2014

Are you using logs on the bind machine\s?


On 03/25/2014 04:31 PM, Jason Brandt wrote:
> We recently migrated to BIND for our internal resolvers, and since the
> migration, we are experiencing periods of high recursive client counts,
> which will at times cause the BIND server to quit responding.  As a
> workaround, I've been able to point the BIND server to a forwarder,
> bypassing the root hints, to restore stability, but this morning even
> with the forwarder, our count spiked.
> We are using Ubuntu 12.04 LTS, BIND version 9.8.1-P1.  The server is
> configured strictly as a resolver, and is not authoritative for any domains.
> We have approximately 15-20k client devices on campus.  Our average
> recursive client count is between 10 and 50.  When the spikes occur,
> counts will get upwards of 3-4k (this morning: recursive clients:
> 2358/9900/10000).
> What are possible causes of high recursive client count?  What can be
> done to prevent this or tune around it?  Obviously raising the max
> clients doesn't solve the problem, and the forwarder seemed to help, but
> apparently is still susceptible to the issue.
> Any suggestions would be greatly appreciated.
> --
> Jason K. Brandt
> Systems Administrator
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