Welcome to our bonus mini episode with a few more “advanced” BBMD topics we tackled!
The response to our Q&A series has been incredible – thank you to everyone who submitted their questions about OT networks and BACnet. Our Co-Founder and CTO, Ping-Pook Yao, tackled some excellent questions about specialized BBMD questions this time around.
Have more BACnet questions? Keep them coming! We love diving deep into these technical topics that help make OT networks more reliable and efficient. Send us a message on LinkedIn, Reddit, or Bluesky, or email us.
If you missed the video, you can watch it [here]. But for those who prefer to read, we’ve summarized the key points below.
Q1: What is a BBMD “Split Horizon”?
In OT networking, specifically for BACnet/IP networks, a Split Horizon BBMD (BACnet Broadcast Management Device) configuration refers to a design approach where broadcast messages from one network segment do not automatically propagate back through the segment from which they originated. Instead, each BBMD selectively forwards broadcasts to specific remote networks, effectively reducing unnecessary traffic and preventing loops.
Q2: When should I use a Split Horizon design?
There’s a few scenarios where a Split Horizon can be helpful:
- If your network has multiple BBMDs forming complex topologies, broadcast loops can occur.
- In larger OT networks with multiple network segments or subnetworks, broadcast traffic can quickly become unmanageable.
- When performance is critical, such as in high-density OT environments or heavily loaded networks, unnecessary broadcast traffic can negatively impact network performance.
- When specific network segments must remain isolated from one another for security or policy reasons.
- When dealing with multiple buildings or locations connected via WAN links, broadcast messages traveling unnecessarily over slow or expensive WAN connections can be costly and inefficient.
- In special cases where there is more than one BBMD per subnet (e.g., redundancy or load balancing), split horizon can help ensure efficiency and prevent unnecessary traffic duplication.
Q3: Port Mirroring: Can I do this on a supervisory device even if I don’t have a managed switch?
Yes! They are independent functions, so feel free to enable BACnet routing (if your device supports it!) in controllers even with a simple unmanaged switch.
Troubleshooting BBMDs
BBMDs can be challenging to troubleshoot, and excessive broadcast traffic is one of the primary reasons building automation systems underperform. Tools like Optigo Visual Networks can help you analyze broadcast message volume and identify problematic duplicate BBMDs quickly.
Have more BACnet questions? Send them our way for future episodes! We love diving deep into these technical topics that help make OT networks more reliable and efficient. Send us a message on LinkedIn, Reddit, or Bluesky, or email us at marketing@optigo.net
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Transcript
Split horizon BBDMD is probably one of the most underutilized, most powerful architectural designs in BACnet systems. Basically not every BBMD knows about every other BBMD and it allows you to focus and reduce the amount of broadcast and where it goes. Basically you can think of it as like hub-and-spoke as opposed to a mesh, where you have one BBMD or set of BBMDs in the middle, and every hub points to the middle. That middle will see the broadcast from all the spokes, but the spokes will not see each other.
So especially when you have a system that’s fairly large, let’s say a thousand devices, The traditional way of ‘every
BBMD knows about every other BBMD’ collapses into one broadcast domain. A broadcast on any device is seen by any device, and now it can create a network that’s quite busy.
So as soon as you have a network that’s a little bit big, or you have a lot of broadcast, contact us! We’ll help you. We should look at using the split horizon methodology to reduce the broadcast, especially in the remote buildings. The remote sites.
BACnet routing can be enabled on supervisor controllers, on BACnet routers, on JACEs, without the need of a managed switch. They’re independent of each other. So yes, feel free to turn on BACnet routing in the controllers even if you have a simple unmanaged switch.
If you have questions around BACnet systems, how BACnet works on other networks, how it works in combination. I would consider us the experts when it comes to that cross section of technology. Send in your questions and we’ll get to it!
