Sonosnet is activated if you connect Ethernet to a Sonos device other than the ERA or maybe the portables. Once it is present it will be used by all Sonosnet compatible devices.

You can connect Ethernet without activating Sonosnet if you disable the radio in the connected device.

I'm thinking Sonosnet is heading for legacy status in the not too distant future so I wouldn't put a lot of work into getting it going, setup your Sonos to use your Wifi instead.

Thanks - I’ve disabled the radio, it was a relatively new Port that is ethernet connected, and it now shows nothing on the status screen. On the other players I now see:

Operating on channel 5540   IEEE channel: 108

Operating on channel 5500   IEEE channel: 100

I have a Velop mesh, and I’m assuming that the top one means one Velop on 5Ghz channel 108 and the other on channel 100… ? 

I’m also wondering if it would be a good idea to reboot the whole system now by unplugging them all and then turning them on in sequence starting with the ethernet connected one. 

Now it appears to (finally) be on the main WiFi, I’m guessing that the STP function becomes much less important? Only the ethernet connected Port is showing any STP stats… On my Cisco switches I have STP classic mode on, but I guess that might be trouble for other stuff. Now thinking perhaps I can get away with RSTP for everything else and configure just the Port port (!) for classic so it at least thinks it’s happy. 

Slightly frustrating that when you setup and select use WiFi that the system doesn’t stick to that of its own accord when you plug something into the ethernet.

Will see how it behaves now.