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BACnet/IP Devices per Channel Limit - Workaround

To configure BACnet to use more than one channel for communications, each channel must use a unique IP Address/Port combination on the TOP Server machine

We have around 140 BACnet/IP devices that we need to connect to on the same channel in an older release of TOP Server. However, the channel limits us to only 128 devices per channel, so we cannot configure the last 12 devices.

Is there any way to configure TOP Server to communicate with the other 12 devices?

First, it is important to note that the device limit was increased to 254 in TOP Server v6.11.718.0. If you are on an active support and maintenance agreement, we strongly suggest updating to this release or newer.

It is possible to configure TOP Server to use more than one channel for communications. The differences with doing this for BACnet, when compared with other Ethernet drivers, is that each channel must use a unique IP Address and Port combination on the TOP Server machine

  • So, either a unique NIC IP Address with the same port,
  • or the same NIC IP Address with unique port number on each physical device

For example, if you were going through a BACnet/IP gateway with 140 downstream devices, the port will likely have to remain the same for all of these devices. So it would be necessary to multi-home the NIC on the TOP Server PC such that it would have 2 unique IP Addresses for each gateway. So if you had 1 gateway, you would need the NIC multi-homed with 2 IP Addresses, if you had 2 gateways, the NIC would need 4 IP Addresses, and so on.

The gateway example above assumes that the gateways being used support multiple concurrent socket connections. If they do not, this workaround will not be a viable option.


The procedure for multi-homing the NIC card can be found in the BACnet driver help file installed with TOP Server, under Optimizing Your BACnet/IP Communications -> Configuring Multiple Channels. You can also view the PDF help file by clicking here.

The alternative, if you can change the port number on the actual physical devices, allows use of the same NIC card on the TOP Server PC. This may be more desirable if it is an issue procuring additional IP Addresses for multi-homing. We would suggest splitting the devices evenly across two channels in TOP Server. You would then need to configure half of the physical devices with a unique Port Number and use that Port Number for the corresponding channel in TOP Server.