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What can I check if SNMP and SSH sensors throw timeout and auth errors?

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In the past, our SNMP and SSH sensors sporadically showed a Down status, throwing timeout and authentication errors without any obvious reasons. Suddenly, many sensor types using SNMP and SSH are Down and show these errors. Now the errors do not turn up again. We did not change anything on the target systems like passwords or private keys. The credentials we defined in PRTG are still correct.

What can be the reason for these SNMP and SSH timeouts and auth errors? How can I avoid these SNMP and SSH sensor instabilities?

authentication error prtg sensor-instability snmp ssh timeout

Created on Mar 26, 2015 4:36:45 PM by  Gerald Schoch [Paessler Support]

Last change on Aug 5, 2019 5:44:05 AM by  Maike Guba [Paessler Support]



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This article applies to PRTG Network Monitor 19 or later

Sporadic Timeouts and Authentication Errors with SNMP and SSH Sensors

SNMP sensors and SSH sensors that switch between the sensor states Up and Down from time to time, showing timeout and authentication errors, indicate a connection instability. This instability can be a result of the configuration of your monitored devices. If you are sure that credentials, passwords, or private keys on the target devices remained unchanged all the time, check other connections that the affected servers might establish.

Look for configurations that devices on which SNMP and SSH sensor are failing have in common. For example, a customer reported that the devices on which the sensors showed the errors all sent syslogs to an external server. First, timeouts happened only sporadically. But after switching off this external server without disabling the sending of syslogs, the sensors permanently showed a Down status.

Turning off the syslog receiver server also resulted in strange behavior of other services on the sender servers. For example, some services needed a lot of time to spawn child services. This also affected SSH. Because this always happened when a new connection was created, it showed up as a timeout or authentication error in PRTG.

In this case, disabling the sending of syslogs to external servers resolved the timeout and authentication issues of SNMP and SSH sensors in PRTG. If you encounter such issues as well, keep in mind when investigating the errors that these can be potential side effects of applications like sending syslog messages from the monitored server.

Created on Mar 26, 2015 4:47:45 PM by  Gerald Schoch [Paessler Support]

Last change on Jul 11, 2019 11:52:29 AM by  Maike Guba [Paessler Support]



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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.