I'd like to use a VPN when on public wifi for security. In order to establish my OpenVPN tunnel I need a working network connection. When I connect to a public wifi access point there is a window of time after connecting but before my VPN client is launched, connects and updates the route table, during which traffic from my system travels unencrypted over public wifi.
How can I cause wifi to pass no traffic except traffic destined for my OpenVPN server during that window of time?
Extra credit : Is there a way to whitelist wifi networks as trusted (like my home or work wifi) such that all traffic is allowed as I won't be using a VPN?