TL> I think there are some corner cases where this is the exception, but TL> mostly, it's IPv6 first by default.
TL> I have an Android app that doesn't like IPv6 enabled in the app on an TL> IPv4 only connection. It doesn't seem to fall back.
If a device is on an IPv4 only connection, it should not even try to connect by IPv6 but just use IPv4. In my dictionary "Fall back" is when an IPv6 connection seems possible and is tried but fails and IPv4 is next.