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SNMP error while trying to add a sensor



Hello everyone, I'm a completely newbie about PRTG monitoring and I'm facing a big, at least for me, problem while trying to setup a monitor for physical disks installed into a QNAP nas. The configuration is the following:

  • the QNAP does have two ip addresses, let's say and, connected through iSCSI to a backup server
  • the server does have three ip addresses, let's say and (for the connection to the nas) and (for the connection to the lan)
  • the core server, where I have installed PRTG, is on a completely different lan (let's say
  • the QNAP see only the addresses on the 172.16.1.x network, he can't reach in any way the 10.x.x.x or the 192.x.x.x networks
  • I have installed the remote probe on the backup server
  • I have installed the tester on the backup server and tested the SMNP replies from the nas, using the Walk option with as parameter, and the nas sent all the data
  • when I try to add a sensor for the physical disks, working on both the core server and the backup server, I get the error "SNMPERR_BAD_SENDTO (SNMP error # -12)"

Am I missing something in the configuration?
Thank you in advance.
Best regards


prtg qnap snmp

Created on Dec 12, 2018 4:09:18 PM

Last change on Dec 12, 2018 7:41:09 PM by  Dariusz Gorka [Paessler Support]

3 Replies



Does this sound about right?

You might have an issue on the remote probe in regards to the outgoing IP here...


Additionally: I do understand you network schema but I would recommend that you have a management IP for the QNAP as well. It is one thing to have it on a separate iSCSI subnet - your IPs are really all over in your example - but I still would recommend you add some kind of management / OOB port / interface to it. A dedicated interface for management only. This also would avoid that you have to use a remote-probe, take care of the outgoing IP in your case and some other stuff - it would even make the device management easier while avoid to have a hub-server that you need to access in order to get to the administrative settings of your storage device. But just an idea of course..


Florian Rossmark


Created on Dec 13, 2018 2:50:38 PM



Hello Florian, first of all thank you very much for your answer! Yes you're right, an additional network interface would be the best choice but actually there's no chance to change the actual configuration, I have already explained that a direct/reachable link to all our Nas would be the best configuration but the policy is that the Nas must be seen only by the backup servers so I'm forced to use the remote probe. I'm out of office right now and I'll be back on next Monday, I'll check that link and I'll report as soon as I'll return. Thank you again. Best regards


Created on Dec 13, 2018 4:52:51 PM



Thank you Florian, as always :)

A unique management IP address is definitely a good idea; then you will need a Remote Probe in the network where that IP belongs to.

Created on Dec 14, 2018 1:17:37 PM by  Isidora Jeremic [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.