Collecting Data from Multi-Subnet BACnet Network

There are many ways a BACnet network can be configured, and Onboard supports more than one way to reach devices across subnets. Onboard can collect data from a multi-subnet BACnet network in two ways: through a BBMD already on the Edge Node's own subnet, or by connecting directly to a controller or BBMD on another subnet.

📘 What is a BBMD?

BACnet devices discover one another by sending broadcast messages across the network. However, these broadcasts do not travel across subnets, which means devices on one subnet cannot automatically see devices on another.

A BACnet Broadcast Management Device (BBMD) solves this. It forwards BACnet broadcast messages between subnets, allowing devices across a multi-subnet network to communicate as if they were on the same local network. BBMDs are typically configured on BACnet controllers or routers by your IT or BMS team.

🔧 How Onboard Supports Multi-Subnet Discovery

The Edge Node can reach devices on another subnet in either of two ways:

• Same-subnet BBMD: If the Edge Node is installed on the same subnet as a BBMD, it will automatically discover all devices that BBMD can see. No additional configuration is required.
• Foreign Address: If the Edge Node is on a different subnet, you can point it at the IP address of a controller or BBMD on another subnet, and the Edge Node will connect to it and discover the devices it knows about. See BACnet Discovery for how to configure a Foreign Address.

✅ What to Confirm Before Installation

If your building has multiple BACnet networks, confirm the following with your IT or BMS team before installing the Edge Node:

• If relying on a same-subnet BBMD: the server or VM where the Edge Node will be installed is on the same subnet as the BBMD, and the BBMD is properly configured with routes to other BACnet networks.
• If using a Foreign Address instead: you have the IP address of the controller or BBMD on the remote subnet, and it's reachable from the Edge Node's network.