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External DNS resolution.



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.

dns public sensor

Created on Dec 2, 2014 5:52:38 PM

6 Replies

Accepted Answer



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.

Created on Dec 3, 2014 4:11:12 PM

Last change on Dec 4, 2014 9:39:12 AM by  Torsten Lindner [Paessler Support]



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

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

Created on Dec 4, 2014 8:49:57 AM



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

Created on Dec 4, 2014 9:37:08 AM

Last change on Dec 4, 2014 9:52:11 AM by  Torsten Lindner [Paessler Support]



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.

Created on Dec 4, 2014 10:14:52 AM



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.

Created on Jul 8, 2016 1:39:19 PM



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.

Created on Jul 11, 2016 11:22:41 AM by  Arne Seifert [Paessler Support]

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.