How to find and solve duplicate networks

Duplicate Webinar
Stop the duplicate networks and get devices back online

Controllers are offline. You try resetting your BACnet router to get them back on. It works, and the controllers come online… But then the controllers off of a different router go offline, and you have to solve the problem all over again.

If you feel like you’re juggling to keep all your BACnet devices online, a duplicate network might be the culprit. We’re here to help you figure out how it happens and what you can do to fix it.

What is a duplicate network?

A duplicate network means there’s more than one BACnet router routing traffic to the same network. There can only be one router per segment, so each router needs a unique network number for each segment. When network numbers get duplicated, you end up with two routers routing traffic to the same network. Router 1 sees all of the controllers on the network, but Router 2 doesn’t. If you were to reset Router 2, it would see all of the controllers, but Router 1 wouldn’t anymore. Hence the juggling. To make things even more complicated, when the router isn’t talking to the controllers that it should be talking to, it causes controllers to go offline as well.

A duplicate network happens when there's more than one BACnet router routing traffic to the same network.

How does a duplicate network happen?

When you first deploy a site, you go in with a network number plan. You lay it out so that there won’t be duplications, and track all the numbers in a spreadsheet. But things change. Misconfigurations, when a new device’s defaults don’t get changed, can lead to duplicate networks. Merging sites together might cause a duplicate network, if you miss changing even one network number. A duplicate network could also happen when there are multiple vendors on a site and no one to coordinate it all.

This is strictly a logical network problem, not a physical one. There’s nothing wrong with how the network is wired, but the misconfiguration leads to duplicate networks.

What are the symptoms of a duplicate network?

The first indication is when part of an entire network segment goes offline. Big red flag. You might try resetting your router to get those controllers back online. As soon as they come on, though, you see that other controllers have gone offline. In reality, the controllers aren’t turning on and off: they’re logically moving around, switching from one router to the other. This flip-flopping is a very common sign of a duplicate network.

How do you fix it?

The easiest way is to go into the network that’s currently online and change the network number. Once you do that, it will communicate with the correct controllers, just like you want it to. The other router will start communicating, and you can reset it too. Congratulations! You have resolved your duplicate network problem.

Make sure you always work with the network that’s online, though. Otherwise you’ll have to fight to get controllers online and figure out which router is talking to which controllers.

When you resolve the duplicate network, routers route where they should and devices stay online.

The main takeaway from this is to have a master plan and stick to it: know what networks you will have on a site and what numbers you use (and where). If things go wrong, always revert to your master plan.

Want to learn more?

Watch our 10-minute webinar below to learn all about duplicate networks!

Recent Blog Posts

November 27, 2018, Vancouver, BC – Vancouver-based Optigo Networks, the network connectivity, monitoring, and analytics company, has released a whitepaper on the future of BACnet and the Building Internet of Things (BIoT).

Gary Brancato had a problem. As a controls engineer at Princeton University, he has a small team and a big campus. It’s just him and his fellow controls engineer Adam, juggling 1,000 Ethernet devices from more than a dozen vendors.

The BAS industry is at a turning point, with IP connectivity shifting the way we see our brick and mortar buildings. 

There are goblins and ghouls that go bump in the night; and then there are BAS misconfigurations that give you a fright! For Halloween, we’ve collected some of your spookiest network horror stories. Read on for stories of:

Have you voted in the annual ControlTrends Awards yet? The ceremony will take place at AHR Expo 2019, in Atlanta, Georgia January 14–16.

Recent Projects

Penn State University Optigo Networks Visual BACnet


When Tom Walker looked at Penn State University’s Navy Yard network, he saw huge issues. The system was busy and loud, to the point where the overrun network was bringing down the entire building. Because this was happening on the MS/TP network, pinpointing the problem would mean boots on the ground to segment and test the chain, piece by piece.

Penn State University Optigo Networks Visual BACnet


When Tom Walker first started working at Penn State University four years ago, there were a lot of network issues. Buildings were dropping offline. Broadcast traffic was pushing 90,000 packets per hour. Walker was on the phone almost every single night because devices were down or had to be reset.


Torre Manacar Mexico City Optigo Connect


When MR Soluciones began work on Torre Manacar, they knew they needed a flexible and scalable network infrastructure to support a wide array of integrated systems. Optigo Networks was a natural fit for the massive project, designing a robust network at a competitive cost.



Short Pump Town Center, an upscale retail center, underwent a complete renovation in 2014. The flexibility of Optigo Networks’ solution meant the retail center’s unknown final design was not a barrier to placing IP surveillance equipment in the field.



Optigo Networks connected New York-based Boulevard Mall’s security surveillance devices in December 2015, using a Passive Daisy Chain topology.

Visual BACnet tech support team


One tech support team at a manufacturer purchased an account with Visual BACnet in April 2017, for technical problems around the world.

Aster Conservatory Green Optigo Connect


The Aster Conservatory Green is a community comprising 352 residences across 24 low-rise buildings. The buildings use advanced surveillance and access control technology, including 40 HD video cameras and 60 FOB-access-tele-entry points for access control.



When Delta Building Automation (Australia) won the BMS Upgrade at 25 National Circuit for the Australian Trucking Association, they partnered with Optigo Networks to create a secure and robust Building Services Network (BSN). Optigo Connect more than delivered on this project with a scalable solution that restored the building network to perfection.

Optigo Connect Seattle Stadium


Optigo Connect offered a simple, cost-efficient solution for a premier Seattle-based stadium. Optigo Networks’ design improved the surveillance system to crystal clear perfection, made it dependable, and allowed the security system to scale with the addition of more than 40 16MP cameras.



Optigo Networks and OTI offered a secure and scalable solution for four data centers’ HVAC and Access Control systems throughout the United States. Optigo Connect’s performance in the first data center was so impressive, the client asked that Optigo replicate the network design for three other data centers.