With some routers/switches it can happen that - e.g. due to hardware changes - the port number of an interface changes. In order for PRTG to continue monitoring the same interface the port number must be changed.

PRTG has a built-in auto-recovery feature that tries to find the new port number automatically, but this kind-of-fuzzy-logic won't always work.

There is no GUI functionality in PRTG's interface to do so, but you can edit the .prtg file (it's XML) manually.

Here are the steps:

• Create a new sensor which points to your new interface using the Create Sensor Wizard
• Save the PRTG file and Close PRTG
• Edit the .prtg file with a text editor
• Find the new sensor: Look for

  <sensor gid="{69FADE87-866A-4C94-AEBB-B293292DB508}">
  <name>
  YOUR NEW SENSORNAME (e.g. Port WLAN-1 on firewall (10.0.0.1))
  </name>

• Find the new sensor's interfacenumber: Look for

  <iface>
  14
  </iface>

• Find the old sensor using the <name> tags
• Edit the sensor's <iface> number
• Save the XML file
• Restart PRTG

Now both the new and the old sensor should be monitoring the same interface.