When bonding the Eras and Sub to the Arc, they connect to a private 5Ghz WIFI transmitted by the Arc for that purpose. So they first connect to your homes WIFI, then while adding them to the Arc they switch the connection. They then become one “room”.
Most router’s network monitoring is pretty weak in detecting the actual connections Sonos is using. As long as your Sonos are working well I’d not worry about what the router thinks.
And the individual devices should still be getting an IP address from the router, but the ‘WiFi’ they’re connected to come from the Sonos soundbar. The IP addressing they’re receiving is via proxy connection.
Strange thing is that the eras, when they were separate showed as connected by ethernet even though they were not.
The Arc is showing up as on 2.4ghz band but the sub is showing as 6ghz (even though I thought 6 was not in the spec).
I am just wondering if this is all as it should be. It seems strange that the sub is still separate.
What you are seeing on your router/AP is the ARP cache. Each Sonos device will have a separate MAC address until bonded, then as said above, IP traffic will be bridged via the soundbar, using the MAC address of Soundbar. I suspect your router/AP management interface is still showing the original ARP, as has not been refreshed. This is normal.
There are situations when this can cause a problem, depending on what network equipment you are using and how it is configured. When updating a Sonos system, the bonded devices will revert to their own MAC, and some network devices may detect this as MAC Spoofing, and block traffic, which will result in the App showing as a failed update, even though it has successfully updated. Although I haven't seen this with the new App recently as much as the old App, probably Sonos has changed timeouts or something in the system update process to provide more robust reporting of updates in new App.
Do you mean your sub is showing as WiFi6 (ax)? WiFi6 can run on 2.4GHz or 5GHz.
