Set up a IPsec/L2TP VPN with Ubuntu 12.04 with OpenSwan, xl2tpd and ppp

This is a guide on setting up a IPSEC/L2TP vpn on Ubuntu 12.04 using Openswan as the IPsec server, xl2tpd as the l2tp provider and ppp for authentication.We choose the IPSEC/L2TP protocol stack because of recent vulnerabilities found in pptpd VPN’s.