What Is a Duplicate MAC Address in BACnet MS/TP?
A duplicate MAC address occurs when two devices on the same BACnet MS/TP network share the same address number.
Since MS/TP is token-based, this causes communication instability.
Symptoms of Duplicate MAC Address
- Intermittent device dropouts
- Devices appearing offline
- Token passing errors
- Unstable point updates
- Network timeouts
How to Diagnose
- Check each controller’s MAC address setting
- Verify address ranges
- Inspect commissioning records
- Use a BACnet analyzer to detect conflicts
How to Fix
- Assign a unique MAC address to each device
- Restart the MS/TP network
- Confirm stable communication after change
FAQ
Can duplicate MAC addresses damage equipment?
No, but they disrupt network reliability.
Is this common after device replacement?
Yes. Address duplication often occurs when new controllers are added without verification.