Easy BACnet
Why am I on the wrong network even though I'm plugged into the switch?
Updated 11 October 2026
A cable in a switch only gets you a link. Which subnet you land on depends on the VLAN that port is assigned to and the IP address you end up with, from DHCP or set by hand. One managed switch often carries the office, cameras, guest Wi-Fi and controls on separate VLANs. BACnet IP discovery only reaches your own subnet, so on the wrong one a scan finds nothing even with the link light on.
What a subnet is
A subnet is a group of addresses that can reach each other directly, without a
router. On most sites you can tell by the IP address: 10.20.30.42 is on
the 10.20.30.x network, and a device at 192.168.1.55 is on a different
one. The two only talk through a router. A BACnet scan only covers your own subnet
(unless the site has a BBMD to pass it on), so being on the wrong one means it finds
nothing.
Why being plugged in isn't enough
In commercial buildings the switches are managed. Each port is assigned to a VLAN, and each VLAN is usually its own subnet. The controls, offices, cameras and guest Wi-Fi can all share one switch. The port you picked decides where you land, and a link light only tells you the cable is good.
Common reasons you land on the wrong subnet
1. The port is on a different VLAN
The most common one. The wall jack or switch port is on the office or guest VLAN. Use a port in the controls panel or JACE enclosure, or have IT move your port to the controls VLAN.
2. DHCP gave you an address from another network
If the VLAN you're on has DHCP, you get a perfectly good address on the wrong subnet.
3. No DHCP answered
Many controls networks have no DHCP server; every controller is set by hand.
A phone or laptop expecting DHCP gives up after a while and picks a
169.254.x.x address, which reaches nothing useful. That's your cue to
set a static address on the controls subnet.
4. A leftover static IP
A laptop still set for the last job's controls network will sit on that address here and see nothing.
How to tell which subnet you're on
Easy BACnet shows the phone's IP address on the scan screen, for example
192.168.1.42. Compare that with the controllers' addresses. If they're on 10.20.30.x and you're on
192.168.1.x or 169.254.x.x, that's why nothing was
found.
How to get onto the right subnet
- Use a controls switch port. Most controls panels and JACE enclosures have a small switch with a spare port. A USB-C Ethernet adapter on the phone gets you onto it.
- Get an address. If the controls VLAN has DHCP you'll get one automatically. If not, ask the controls contractor for a free static IP address in that range (an address like 10.20.30.250 that nothing else uses). Not every Android phone lets you set a static IP on a USB Ethernet adapter, so check yours before you're on site; a laptop or small travel router set to the static address is a common workaround.
- Ask about a BBMD. If the site has one, Easy BACnet can register with it from another subnet and discover through it.
- Add a known device by IP. If a controller's address is reachable through a router, Add device by IP… in the menu goes straight to it.
What to tell IT or the controls contractor
Three things usually settle it quickly: the IP address Easy BACnet shows for the phone, the subnet the controllers should be on (if you know it), and which switch and port you're plugged into. That tells them straight away whether you're on the wrong VLAN.
Check it on your own network. Easy BACnet is a free Android app that finds BACnet IP devices and reads their points in a couple of taps.
Get it on Google Play