Say for example you have 2 active network interfaces on your computer. In my case, 1 is for the Ethernet Cable and the other is for the USB via Tether.
The LAN Cable connection has no Internet connectivity but I need to make my computer belong to the network (since I am running a particular network application). Since I need to have an Internet connection, I used my mobile phone and shared my Mobile Data connection via USB Tether. I want to use both connections simultaneously.
I did the following to solve the problem:
1. Open Network Connections
2. I selected the connection where there is NO INTERNET and clicked on Edit.
3. Go to the IPv4 Settings Tab and click on the Routes button.
4. I just checked on the following settings: a) Ignore automatically obtained routes and b) Use this connection only for resources on its network.
Make sure to be connected to the two networks.
To verify if your configurations have worked, you can use the traceroute command to trace the routes of a certain ping.