Thank you for contacting Intel Communities.
In this case, there aren't any settings in the BIOS that you can change to have both connections working at the same time as it is more related to an OS configuration. However, I found some 3rd party websites that you may find useful:
How to Wifi And Ethernet At the Same Time - Tomshardware
How to select default network interface for internet? - Superuser
NOTE: These links are being offered for your convenience and should not be viewed as an endorsement by Intel of the content, products, or services offered there.
I hope this information helps.
Please don't hesitate in replying to this post if you need further assistance.
Hello. Both hints do not work out. There is some automatic mechanism that enable WiFi if the ethernet cable is not connected. If I plug in the network cable WiFI is automatically disabled. Some pages in the internet told me that this is due to a setting in the BIOS which I do not find in the BIOS of my NUC. If it is an OS issue where can I go rid of this behavior? OS is Win8.1.
At BIOS level there isn't any restriction for both controllers (LAN & WLAN) to be active at the same time; you can disable any of both controllers in the BIOS, however; it will cause that specific controller not to work at all until you enable it again.
At this moment I would recommend contacting Microsoft so then you can get information about the changes you may need to apply to the OS.
Hope this information helps.