L2TP VPN prevent other connections

Hi guys,

I have the following issue:
I have to use a L2TP-VPN connection with a preshared key so that my IP address/location does not get revealed.
How can I achieve the following 2 functionality with the first one being more important:

1.) Prevent all non-VPN connection to the internet

2.) Automatically reconnect to the VPN if the connection is lost

Thank you very much for your help in advance!