Monitoring STP changes with PRTG

PRTG is my recommended monitoring solution for small-medium businesses. It is easy to install & setup on Windows and is free for up to 100 monitors. This requires a managed switch.

STP or Spanning Tree Protocol is a Layer 2 switching protocol used to prevent loops (loops cause broadcast storms) Small companies don’t have the expertise to understand STP or set it to act in a predictable manner.

This monitor can at least confirm STP changed and that’s why the network went “wonky” for a minute. And you can yell at whoever is plugging and unplugging cables.

If you don’t have one already, add a device and set the address to your main switch. PRTG usually discovers your main switch automatically.

From the devices screen, right click your main switch and choose Add a sensor. Click SNMP Custom as the sensor type

Add a senor name, OID value is

Divide by 6000 to get a value in minutes. you could divide by 360000 to get a value in hours but then you might get an overwhelming amount of alerts when it triggers.

If you want an email notification when this is triggered, right click your new sensor, choose edit, and Notification Triggers

In the Top pane click the plus sign and Add Threshold Trigger, fill in our threshold values of below 1 minute for 1 second, send and email to whoever. no email when resolved. In the pane below choose “only triggers from the top pane” as we don’t care to get an alert when PRTG fails to read the SNMP entry.

All done. your email alert may be delayed as PRTG is trying to send the alert while your network it trying to re-converge.