Circular Networks: Detecting and solving them in your BACnet System

Circular Networks BACNet Visual BACnet
Detect, Understand and fix Circular Networks in your BACnet or Building Automation System

A Circular Network will quickly wreak havoc on your BACnet system. We’re here to help you figure out how it happens, how you can identify it and the steps you need to take to fix it.

What does a Circular Network look like?

In order to end up with a circular network, you must have multiple IP to Ethernet routers. They can be from the same vendor or different vendors, but they will be on the same network. A circular network is as easy as enabling both protocols with a simple checkbox on both controllers.

Circular Network in your BACnet Building Automation System


How does a Circular Network happen?

A circular network happens when you have two (or more) routes to the same controller.

Typically, the routes are BACnet/IP and BACnet/Ethernet and both are communicating on both networks. This could happen with BACnet MS/TP although it is more rare. In many cases, enabling both protocols is as easy as checking both check boxes on the many manufacturers controllers.

Often Circular Networks happen when migrating a site from Ethernet to IP. It’s easy to accidentally have two routers speaking both IP and Ethernet at the same time during this process. Another common cause is if you are keeping the Ethernet network because it is easy to connect to.

What are the symptoms of a Circular Network?

A circular network causes any message transmitted on the network to continue being transmitted over and over, resulting in so much traffic the network is clogged and the controller is so busy servicing the network, that it can’t do anything else. The following are some common signs and symptoms of a circular network:

  • Controllers are unreachable
  • Network is inaccessible if you connect through the controller
  • No or limited data exchange is available from the controllers
  • Controller is not executing any functions
  • Reduced network bandwidth
  • MS/TP devices aren’t responsive as the routing controller can’t service the network
  • BMS is functioning slowly

How do you find it?

First, you need to identify the routers that are causing the circular network. This can be done in Wireshark (see our Advanced BACnet Troubleshooting in Wireshark webinar), or in Visual BACnet. Simply capture network information in a PCAP file, upload it to Visual BACnet, and you will see the Circular Network diagnostic check fail. Click on the diagnostic check to see which devices are causing the circular network.


How do you fix it?

Your circular network will be causing such a traffic storm that you won’t be able to reach any of the controllers. To fix it you will need to unplug one of the problematic controllers, isolate it from the network and reconfigure it. You can then add it back onto the network.

Want to Learn More?

Watch our 10 minute webinar below to learn all about Circular Networks!

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