|GNOME's gnome-session-properties tool.|
Facing this dilemma when working for a couple days on a nest of layered networks an obvious solution presented itself. I simply set all networks to not connect automatically. Simple - yet annoying. Because now every time I login I have to the GNOME Control Center's Network tool and select a network. That step gets old when you have to do it almost every time you login. But a simple solution to that is also available - setup the Network tool to launch upon login.
|GNOME's Network Control Center tool.|
Now nothing gets connected automatically but connecting, if desired, is only a click or two.