Read The Part 1: Duplicate MAC Addresses / Device Instance
For Example:
- Device A has the MAC address of 0x03 Node ID 7
- Device B has the MAC address of 0x04 Node ID 7
- Device C has the MAC address of 0x05 Node ID 13
- Device C sends a broadcast request for the properties of Node 7
- All devices on the network receive the message and Device A and B start to compile a response
- Device C sends the token to the next device in line, this happens to be Device A
- Device A responses to the poll from Device C and passes the token to Device B
- Device C processes the response
- Device B responses to the poll from Device C and passes the token to Device C
- Device C gets the response from device B and overwrites the results of device A
So in conclusion, having two BACnet MSTP devices with the same MAC address will produce unpredictable results and should be avoided. While having two BACnet MSTP devices with different MAC address and the same node ID will produce a predictable result it should be avoided because of the rule (no two devices shale have the same Device ID)
Read the 2 BACnet MSTP devices with the same device ID article.
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