It depends™:) Yeah, if you have a dumb switch with devices plugged in, then the upstream router probably isn't relevant. But if you've got all devices on wifi r

It depends™:) Yeah, if you have a dumb switch with devices plugged in, then the upstream router probably isn't relevant. But if you've got all devices on wifi running through a single box that's a router+switch+WAP+modem (very common in consumer home networking) then that single network box is in an excellent position to control devices talking to each other. YMMV.