[Pdns-users] Occasional TCP query timeouts.

Peter van Dijk peter.van.dijk at netherlabs.nl
Mon Oct 3 05:49:11 UTC 2011

Hello Grant,

On Sep 30, 2011, at 7:12 PM, Grant Keller wrote:

> We have been having this problem with TCP queries timing out on one of our nameservers running pdns 3. We have a monitor that runs every two minutes, and every half hour or so it times out on its query. I can reproduce this by  running the following:
> while [ 1 ]; do
> dig schwer.us +recurse +tcp +short +time=1 +retry=1 @c.ns.sr.sonic.net
> date
> sleep 1
> done
> If I let that run for a while, it will capture several timeouts:
> ; <<>> DiG 9.7.3 <<>> schwer.us +recurse +tcp +short +time=1 +retry=1 @c.ns.sr.sonic.net
> ;; global options: +cmd
> ;; connection timed out; no servers could be reached
> The pdns.log has no significant entries at the times that this occures. I have watched iptraf as I recieve the timeouts, and It dosn't seem that we are hitting our max number of tcp connections (1000). This problem first started in pdns-2.9.22, and continued after the upgrade. None of our other name servers have this problem.
> What would be the next step in troubleshooting this? Are there any extra logging options I can turn on? Thanks in advance.

Most important to know, of course, is whether the queries even reach pdns. Are you in a position to run tcpdump/tshark on c.ns.sr.sonic.net, to monitor requests from a test run like the one described above?

Kind regards,
Peter van Dijk

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