If you have a very large site, multiple BACapps can be installed on the site to manage the BACnet devices. Each BACapp will need to be installed on its own PC.
On the BACnet Settings page you're able to set a limit to the range of device instance numbers the BACapp will look for during a site discovery. For example, one BACapp may look for instance numbers from 1-1000 while another will look for 1001-2000. Use as many BACapps as needed to be able to discover and group all BACnet devices present on the network.
The default value for Instance Number Discovery High Limit and Low Limit are both -1. This means the BACapp will search for all device instance numbers. If you enter a value in either field, you must enter a value in the other field as well to set a range.