Duplicate BBMD Detection

Overview

• A BACnet Broadcast Management Device (BBMD) sends a unicast message from one BACnet or IP device on a subnet to other subnets.
• When the message gets to the destined subnet, the message is rebroadcast.
• In a duplicate BBMD, multiple devices on the same network are set as BBMDs, and are rebroadcasting the same messages.

Why it fails

• A setup issue, typically on a mixed vendor site.
• The first vendor sets up multiple networks and connects them with BBMDs.
• A site upgrade or change takes place, a new vendor wins the contract, and they add devices to each network.
• To connect the devices, they put a BBMD on each subnet.
• This can continue, resulting in two, three, or more BBMDs on each subnet, and double or triple the traffic. There should only be one BBMD per network.

How to fix it

• Find all the problem vendors using the IP addresses, vendor identifier, and MAC address in Visual BACnet.
• Isolate networks if you don’t need integration.
• If not, assign one vendor and their BBMDs to the task.
• A good rule of thumb is to use one vendor’s BBMD, as it’s easier to make site-wide changes.