Thanks, but unfortunately it does not apply.
Running Windows 10, very simple network, with just the standard subnet configuration.
Tried both a laptop, and desktop, plugged into the same switch as the BRX, with DHCP running on the router.
It is as if the hardware side of the Ethernet is working, but not the software in the BRX, as if the port was not configured...
This is a new unit out of the box, first time being powered up.