How to set-up VPN server using IPSEC and L2TP in Debian 7 (Wheezy)

How to set-up VPN server using IPSEC and L2TP in Debian 7 (Wheezy)

The following article covers the steps I used to install and configure a VPN server using IPSEC/L2TP over PPP on a Debian Wheezy system. I'm using it in my Nexus 4 running Android SlimKat and I use other GNU/Linux machines as clients to connect to the VPN server. This allows me to securely communicate between the machines in my own virtual private network.