I'm not a very experienced Linux user but I've managed to setup a connection to a VPN using OpenVPN on my Raspberry Pi 2 Model B running Raspbian Jessie. So I've got a eth0 and tun0 interface running.
Basically I want to close its connection to the Internet when or if the VPN shuts down. Like a kill switch. I've seen some solutions using iptables or setting up default routes but I cannot seem to understand how they work, and therefore I can't apply them to my problem.
How would I achieve this?