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DNS Server Does Not Respond

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Hi Team

Do you have a standard troubleshooting procedure for the “DNS Server Does Not respond” errors.

This happens 2-3 times weekly on one of our probes… it always seems to happen at around the same time – 8-9am. And we get a flood of around 50-60 sensors with this error.

We don’t see any DNS resolution issues at the same time

What kind of things can we use to narrow down the error e.g. for a particular sensor..? I can probably get wireshark installed on the machine.. so should I be looking for DNS queries that are not being replied to? Can you give me some idea of the code path that results in these error messages?... i.e. what the code expected to be able to do that failed (DNS lookup, TCP connectivity to device..)

dns-resolution probe tcp

Created on Mar 6, 2020 8:17:56 AM by  trunq (11) 1



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Hi there,

To resolve this issue, check if the DNS service on the remote host may be shut down. Also check if a firewall or IPS between the monitoring server and the remote host is sending a reject for the connection.

If you cannot further information there, I would recommend to analyse this further with an analyzing tool like Wireshark. With this you should see, if the requests are sent correctly.


Kind regards,
Birk Guttmann, Tech Support Team

Created on Mar 9, 2020 1:01:10 PM by  Birk Guttmann [Paessler Support]



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I have the same problem since 2 weeks ago!

Created on Jun 29, 2020 9:16:16 AM by  amajoura (3) 1



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Hi there,

Did you already followed the suggested troubleshooting steps?

Created on Jun 29, 2020 9:29:27 AM by  Moritz Heller [Paessler Support]



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Yes, i did, i have this error only with sql sensors

Created on Jun 29, 2020 9:51:23 AM by  amajoura (3) 1



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Did you already checked whether you can make a nslookup from the Probe server about the target device?

Created on Jun 29, 2020 10:06:53 AM by  Moritz Heller [Paessler Support]



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Can I install Wireshark on the core (PRTG)server without problems?

Created on Jun 29, 2020 10:07:39 AM by  amajoura (3) 1



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The Core and Probe are installed on the same server. A nslookup tot the target replies correct.

Created on Jun 29, 2020 10:10:03 AM by  amajoura (3) 1



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Hi there,

Since the issue doesn't appear on a regular basis, it is hard to troubleshoot that way. Please also make sure that the FQDN is configured for the parent device, since it is more reliable for Windows related queries.

​ Using Wireshark is a good idea here. It should work without issues on the PRTG Server. Please let us kn ow if you could see any interference there. ​


Kind regards,
Birk Guttmann, Tech Support Team

Created on Jun 29, 2020 10:17:32 AM by  Birk Guttmann [Paessler Support]

Last change on Jun 29, 2020 10:17:46 AM by  Birk Guttmann [Paessler Support]



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once a day, all the sensors (+/- 2500) get the status "unknown" for a while, when refreshing, the number decrements. This is also since 2 weeks ago.

Created on Jun 29, 2020 3:54:50 PM by  amajoura (3) 1



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Hi there,

This seems to be a new request, isn't it?

Please also note that this is a Knowledge Base, which is built to share information or issues that may be interesting for other customers. If you have issues with PRTG you can also open a support case by writing a mail to "[email protected]".


Kind regards,
Birk Guttmann, Tech Support Team

Created on Jun 30, 2020 8:51:51 AM by  Birk Guttmann [Paessler Support]



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Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.