This article applies to PRTG Network Monitor 17.4.35, 17.4.36, and 18.1.36.3728

Known Issue: Wrong Data Scaling in SNMP Library Sensors

PRTG version 17.4.35 that we released in November 2017 came with several improvements for the SNMP Library sensor, but we got reports about incorrect data scaling in newly created SNMP Library sensors.

Note: SNMP Library sensors that you add in PRTG version 17.4.35 or later will be created as SNMP Custom Advanced sensors, SNMP Custom Table sensors, or SNMP Custom String sensors.

What is the Issue?

Under certain circumstances, newly created SNMP Library sensors display monitoring data with a wrong scaling. This means that the decimal separator is on the wrong position. In some sensor channels, you will see much higher values than the ones that were actually measured.

In PRTG version 17.4.35 we changed the way the SNMP Library sensor evaluates the unit of a channel. The goal was to have the precise unit of the specified counter, but this approach results in an issue when there is a scaling that is defined by an MIB. PRTG correctly reads the scaling from the device but currently it is incorrectly evaluated by the PRTG core server.

Example: The SNMP Library sensor shows the value 2251 in a sensor channel instead of the correct value 22,51 (or 22.51).

Note: Depending on the language version, the decimal separator either is a decimal comma (22,51) or a decimal point (22.51).

What are the Implications of the Issue?

The issue only affects SNMP Library sensors that you newly create in an affected PRTG version and when the imported OID library (OIDLIB) assigns a unit that is not Custom.

Affected sensors will show wrong values in gauges, graphs, and tables, for example. If you have set limits in the sensor channel settings, the limits will also apply to the wrongly displayed values.

Note: Raw monitoring data is not affected by the issue. PRTG reads the correct values from the target device but displays them in a wrong way.

Which PRTG Versions are Affected?

The issue affects PRTG versions 18.1.36.3728, 17.4.36.3670, 17.4.36.3595, and 17.4.35.3441. PRTG versions before 17.4.35 are not affected.

SNMP Library sensors that you have added to PRTG before updating to version 17.4.35 or later are not affected and show correct data.

When will You Provide a Fix?

We will provide a fix for this issue in one of the next PRTG versions, please bear with us! Once a fix is released, you will find an according entry on the PRTG release notes.

Do I have to consider anything when updating to the fixed version?

In the PRTG version that includes the scaling fix for the SNMP Library sensor, the values of the SNMP Library sensor will automatically use the correct scaling again and show the decimal separator on the correct position after you have updated PRTG.