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How to find and solve duplicate networks

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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.

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.

Duplicate Networks

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.

Duplicate Networks

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!

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