What this means
The IEEE assigned the MA-L block D490E0 to Wachendorff Automation GmbH & CO.KG. Every network interface they manufacture under this block has a MAC address beginning with these digits, followed by a unique per-device identifier. If a device on your network shows a MAC starting D4:90:E0, it is Wachendorff Automation GmbH & CO.KG hardware.