I'm working on the latest raspberry pi os, which I believe is Debian based.
I'm running the minimal (no gui) version, but can install additional packages if required.
I want to have a pi connected to a single device over ethernet. The pi will be 10.0.0.1, and the device will be 10.0.0.2.
The pi and the device both need outside internet access. The pi will be connecting to the internet via either wifi or modem connection.
In order for the ethernet device to get internet, I believe I need to set up a bridge between the ethernet, and the wifi and modem.
All the individual parts are working independently. The pi can ping the device on 10.0.0.2, and ping google.com via the wifi or the modem (whichever is up, and if both are up the wifi is used). The one piece lacking is the ethernet device can ping 10.0.01, but can't ping google (ie no outside connection)
My understanding is that networkmanager (In my case using nmcli) is the high level process that is supposed to handle bridging setup etc.
I have spent hours looking at examples and trying to get any bridging working via network manager. I am not able to get it to bridge between the ethernet and the wifi, let alone start attempting to make it also work with the modem when that connection is up.