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My IP on DNS Blacklist sensor does not work anymore. What can I do?



My IP on DNS Blacklist suddenly stopped working. The last message says that there is an “error checking dnsbl.njabl.org” and that the host is unknown. Why does this happen and how can I get this sensor back to work again?

blacklist error hotfix ip-on-dns-blacklist-sensor prtg

Created on Apr 30, 2013 12:32:40 PM by  Gerald Schoch [Paessler Support]

5 Replies

Accepted Answer



IP on DNS Blacklist Sensor: Hotfix for “Error checking dnsbl.njabl.org” (Unknown Host)

The reason for this suddenly appearing error with the IP on DNS Blacklist Sensor is that the blacklist server dnsbl.najbl.org was shut down recently. By default, PRTG uses this server if the Blacklist Servers field is left empty. Please specify another blacklist server used for the blacklist check in the sensor settings.

Steps to Go

  1. Go on the details page of your existing IP on DNS Blacklist sensor(s)
  2. Choose the Settings tab.
  3. In section Sensor Settings, enter a (new) blacklist server.
    We recommend using bl.spamcop.net
  4. Click on Save.

The sensor will begin to work again immediately, using the new blacklist server.

Created on Apr 30, 2013 12:36:35 PM by  Gerald Schoch [Paessler Support]



The instructions indicate that I can have a comma-separated list of blacklist services. When I try that, the sensor fails. Is this a known bug or do I just have the syntax incorrect?

Created on Apr 30, 2013 6:48:09 PM



a comma separated list is possible but please make sure that no whitespaces are in the list, like:


Best regards

Created on Apr 30, 2013 6:54:34 PM by  Konstantin Wolff [Paessler Support]




We have moved all our sensors onto the new Blacklist server and we are getting Last Message Ok Last Result 0 #

However, this is also the case when we enter www.google.com as the Blacklist server, as well as when using our own website server (which I know is not doing any sort of blacklist check).

Created on May 6, 2013 6:13:57 AM



Dear James,

I agree that this can look confusing although technically the result is correct.

The sensor works as expected: As www.google.com is not a blacklist server, the given IP is not listed, so the result is 0.

Please make sure you enter one or more valid blacklist servers in the sensor's settings.

Created on May 6, 2013 10:49:00 AM by  Daniel Zobel [Product Manager]

Last change on May 6, 2013 10:54:15 AM by  Gerald Schoch [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.