How to resolve Duplicate Device IDs

Learn how Visual BACnet can help you find and fix Duplicate IDs on your network
Solving Duplicate Device IDs in Visual BACnet

It’s super important to have unique Device IDs on your BACnet system, but duplicates are a very common problem. Unfortunately, you might not even realize you have duplicate IDs, with devices only responding periodically.

While they may seem like an obvious issue to avoid, finding duplicate IDs can be difficult. Find out how Visual BACnet helps you quickly isolate duplications, so you can focus on fixing the problem. Watch our webinar below, and read on for the recap!

Duplicate Device IDs could arise a number of ways — perhaps someone copy-pasted the configurations from one subnet to another, or a preset wasn’t updated — but the result is that you have two or more devices with the same ID. 

Let’s take an example where a temperature sensor and a controller both have the ID 1121. When we send out a Who-Is for Device 1121, both devices will respond. 

Duplicate Device IDs

Duplicate Device IDs



Whichever device responds first, the BMS will recognize that device as 1121. In this case, the Temperature Sensor has responded first. 

But this won’t necessarily always be the case. The next time that the BMS sends out a Who-Is, maybe the Controller responds first and the BMS marks that device as having the ID 1121. 



Duplicate Device IDs

Duplicate Device IDs

This issue might not be so significant in the case of simple Who-Is requests and I-Am responses. But let’s say the BMS is asking Device 1121 for the Present Value of Object 27. Well, the Controller also has an Object ID 27, so it’s going to respond to that request with its own Present Value. In this case, the value is 80. 



Duplicate Device IDs

Duplicate Device IDs

The BMS now thinks the Temperature Sensor is reporting a temperature of 80° Fahrenheit, so it will respond by cooling the room. 

Duplicate Device IDs

But the value of 80 wasn’t in degrees Fahrenheit (maybe it was humidity), or even if it was, it’s for a different room, so you’ll likely end up with tenant complaints that the room is too cold. 

This leads to a constant back and forth between heating and cooling the room as the two devices report different values to the BMS. Tenants are unhappy, you use more energy than you needed to get an ideal room temperature, and when you’re brought in to fix the problem, it’s going to be really hard to find the source. 

You can use Wireshark to scroll through, filter, and isolate the Duplicate Device IDs, but it could take a couple hours. Instead, Visual BACnet points you right to the problem. Just upload a pcap file to Visual BACnet, and if there are Duplicate IDs on your network you’ll see it under the Diagnostic Checks. 

Duplicate Device IDs

Click on the Duplicate Device ID row, and Visual BACnet will show a list of the IDs as well as how many times they were spotted on the network. 

Duplicate Device IDs

Simply correct the IDs of the devices, ensuring there are no duplications, and you’re done! 

We hope you learned a lot from this session on Duplicate Device IDs. Watch more videos on solving BACnet problems in our video playlist, and subscribe to our YouTube channel to stay up to date on other educational webinars!

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