By default devices residing in different subnets will not be discovered as the standard discovery mechanism uses broadcasts into the local subnet. Therefore devices residing in different subnets will not show up without additional configuration since broadcasts don't cross routers thus are not forwarded into different subnets.

Note: To discover devices residing in different subnets the IPv4 address of these devices must be known upfront.

Using IPConfigure's "Setup Unicast Device Discovery Destinations" dialog allows to specify the known IPv4 address of each device which shall be discovered in a different subnet.

Select the "Action" menu item and click on "Set Up Unicast Device Discovery".

IPConfigure - Action menu
A dialog will open, where the destination IP addresses of the devices to be discovered can be entered.
Select the interface through which the devices in the different subnet will be reachable by using the "Interfaces" drop-down menu. This interface must be able to reach the target subnet of course so has to be connected to the corresponding router and/or switch.
Enter the IPv4 addresses of devices which shall be discovered.
Note
Once the desired IPv4 addresses have been entered the "Discover" button can be used to detect those devices. If a device is found the corresponding row in the grid will be marked in green and the serial number of the discovered device will show up in the discovered column. If a device is NOT showing up make sure the IPv4 address you have entered is correct and the interface selected for detection is actually capable of reaching the desired subnet.

IPConfigure - Setup Unicast Device Discovery Destinations
Click on "Apply" button.
The dialog will be closed and IPConfigure as well as every other application using the Impact Acquire driver stack will be able to discover and use devices at the previously entered IP addresses.

IPConfigure - Device discovered in a different subnet

To modify the settings the dialog can be used. To disable the device discovery in different subnets just select the correct interface and clear the table using the "Clear" button.

Note: The settings for detecting devices in different subnets will be permanent for every application using Impact Acquire on the given system. There is also a set of API properties that can be used to implement the same behaviour. In fact IPConfigure uses this API internally. To implement this in your own application have a look at the InterfaceModule class. The properties starting with mvUnicastDeviceDiscovery will provide the required features.