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..)

Article Comments

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


Mar, 2020 - Permalink

I have the same problem since 2 weeks ago!


Jun, 2020 - Permalink

Hi there,

Did you already followed the suggested troubleshooting steps?


Jun, 2020 - Permalink

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


Jun, 2020 - Permalink

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


Jun, 2020 - Permalink

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


Jun, 2020 - Permalink

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


Jun, 2020 - Permalink

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


Jun, 2020 - Permalink

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.


Jun, 2020 - Permalink

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 "support@paessler.com".

Kind regards,
Birk Guttmann, Tech Support Team


Jun, 2020 - Permalink

Hi we also have this errors for 2 days now. It happens on SQL sensors and some custom EXE sensor. restarting the PRTG server resolve these error for abour 24 hours... but then errors came back.


Jan, 2021 - Permalink

We have the same issue on custom EXE/XML (PowerShell) sensors. It works again after a reboot... The same issue does occur a couple of hours later. How can we fix this problem?


Apr, 2021 - Permalink