Hi everyone,

I'm wondering if it could be created a sensor for external DNS resolution that avoid to get an answer; in my DataCenter the reply for this DNS's is not allowed and therefore the sensor I create is not enough.

For example, my windows-based DNS server is configured in order to ask to resolver1.opendns.com for external DNS resolution but the reply for the ping is filtered by our firewall so I will never get a reply for this public DNS, only a name resolution. Therefore my sensor returns always a fail.

Thanks for your help.

Article Comments

PTF.CheckDNS as a Custom Sensor is a wrapper for 'nslookup'.

Using the parameters

-h=   name of the host to lookup.
-s=   name of the DNS server to use.

You can check the response of a DNS server.

For example -h=google.com -s=resolver1.opendns.com will return 1 (one) if the lookup succeeded and 0 (zero) if the lookup failed.

Using limits on the sensor's value channel, you can set the sensor to a warning or error state when the lookup fails.


Dec, 2014 - Permalink

Thanks for your answer, that seems to be exactly what we need!

Unfortunately the link you provided is not working, for me at least...


Dec, 2014 - Permalink

You are right, the http:// part was missing, causing the KB system to treat it as an internal link.

The complete url is: http://prtgtoolsfamily.com/?page=downloads_sensors


Dec, 2014 - Permalink

Finally I get the sensor, added to the probe and configured as you pointed. It works like a charm.

Thank you very much for your help.


Dec, 2014 - Permalink

Checkdns Always gives an OK. Even for not existing hostnames.

I also tried the dns sensor, but this also gives an error: Connection reset by peer Socket Error # 10054 Connection reset by peer. (socket error # 10054)

The sensor is active on a mini probe that runs on a server in DMZ with access to internet. I am trying to check if an A record exists of an external host.


Jul, 2016 - Permalink

Dear Frank

I am sorry, while offered by Paessler as a reference implementation, the mini probe is not covered by technical support.

You might want to use a custom SSH script instead, so you have full control over the DNS check.


Jul, 2016 - Permalink