Internet over mobile-data while connected to WLAN network I have a WLAN network that is not connected to the internet. There is a DHCP server on that network and that assigns its clients an IP and subnet mask, but no default gateway.

When I connect to this network on an android device mobile data will automatically be disabled, so that the device will loose internet connectivity.

Most operating systems, when they are connected to multiple networks use the fastest connection that has a default gateway to connect to IP outside its respective subnet. However Android doesn't seem to get to that stage, because once it connects to a wi-fi network, it will disconnect the mobile-data - to save battery power, presumably. It doesn't care to check if there is gateway on the wi-fi network.

Is there a way to disable this "feature" of disconnecting mobile data when a wi-fi is connected?

Or better: is there a way to prevent disconnecting mobile data when the wi-fi has no default gateway?

Thank you in advance.
First, you need a rooted device. 

Then, have a look at this, it's maybe what you're searching for.