Duplicate BACnet Broadcast Management Device (BBMD)

Overview:

The "Duplicate BBMD" diagnostic alerts when two or more BACnet devices acting as BBMDs are forwarding BACnet broadcast messages from the same subnet to the same subnet(s). While having two BBMDs on the same segment isn't strictly a problem, having two or more BBMDs forwarding traffic from the same source to the same destination network segments will multiply the amount of broadcast traffic.

Each device is forwarding broadcast traffic from the same network segment. If two BBMDs are routing that traffic to the same destination, your network is unnecessarily doubling the amount of traffic being generated. The issue is further compounded by any additional BBMDs on that segment.

Causes:

• Configuration errors: Two or more BACnet devices designated as BBMDs on the same IP subnet are forwarding traffic to the same destination IP subnet. 

Implications:

• Communication Errors: Intermittent communication errors or data collisions on the network can lead to delays in message delivery and response.
• Network Congestion: Heavy OT network traffic or congestion can lead to delays in transmitting and receiving BACnet messages, resulting in slower response times.
  
• Device Overload: If a BACnet device is handling a high volume of requests or tasks, it may not be able to respond promptly, causing delays in response time.
  
• Device Latency: Some devices may be prone to longer response times due to their processing capabilities or network positioning.
  
• Network Latency: Geographic distances between devices or the presence of multiple network segments can introduce latency in communication.
  
• Network Quality: Poor network quality, including low signal strength or unstable connections, can contribute to slow response times.

How to Fix It:

• Use OptigoVN Site Scope(s) to identify the addresses of all devices acting as duplicate BBMDs. Reassign those devices with a new unique device address. Re-test to ensure the issue has been resolved.
• Edit the BBMD distribution table (BDT) of the devices to keep only one BBMD forwarding traffic to and from that segment. The BBMD function can be disabled on one of the devices if BDTs are the same. If the BDTs are different, ensure there are no duplicate BBMD device IP addresses as destinations.
• Documentation: Maintain up-to-date documentation on device assignments and changes to prevent accidental duplicates.
• Configuration Review: Regularly review and verify device configurations to ensure no duplicate devices have been configured as BBMDs.
• Training: Ensure personnel involved in device configuration and management are aware of the importance of unique device addresses.
• Regularly perform diagnostic testing with OptigoVN to reduce issues associated with duplicate BBMDs.