Yast -> network devices -> network settings -> interface -> activate device

Currently there are several options, like on boot, on cable connection, manual, etc.

Let's focus on cable connection -- when cable is connected that device is activated. That is what this option says. But what this option _does not_ say is this activation is exclusive, i.e. it will shutdown all other active interfaces.

I am not discussing if such implicit, additional action is useful or not (for me not), but anyway, if there is an _extra_ action, there should be an _extra_ option. Namely:

[ ] exclusive activation

that way user could set/control if she/he really wants exclusive connection over only one interface. This way also it would be finally possible to use "on cable connection" settings with multiple interfaces/connections (currently it is not possible and user has to set it up manually with ifup).