This article applies as of PRTG 22

QNAP SNMP DoS alarms and system information

With certain QNAP firmware versions, you might receive the alarm [SNMP] DoS detected when using the System Information feature. This is not an error in PRTG but is instead caused by a setting on the QNAP itself.

The System Information feature scans your PRTG installation once every 24 hours to show all available system information data for your devices.

The QNAP has a built-in DoS checking feature that defaults to 300 SNMP packets per second. This limit can be easily reached when using the System Information feature.

SNMP monitoring with QNAP and custom sensors might also trigger this alarm. This might be because of issues with certain QNAP firmware versions, for example 4.3.3 or 4.3.4. See the QNAP forum for more information.

Solution 1: Disable DoS detection

Important: Make sure that this solution is in line with your company's security policy before you disable DoS detection.

If you do not want to receive the [SNMP] DoS detected alarms, you can disable the DoS detection in the QNAP's settings. Simply run the following command.

# setcfg SNMP EnableDetectDDoS FALSE

Then you need to restart SNMP.

# /etc/init.d/snmp restart

Alternatively, you can also increase the maximum number of requests using the following command.

# setcfg SNMP MaxPacketPerSecond XXX

Solution 2: Disable system information

If you do not want to disable DoS detection, you can disable the System Information feature in the PRTG web interface.

1. In the device's settings, go to the Advanced Network Analysis section.
2. Under System Information, select Disable.

System information is now disabled for the device.

Solution 3: Disable disk hibernation

To disable disk hibernation, proceed as follows: Go to Control Panel | System Settings | Hardware | HDD Standby, and disable it. Afterwards, the sensors should work without further issues.