This whitepaper discusses OpenVPN as a free, secure, and easy to use and configure SSL-Based VPN solution. It offers various scenarios of use.
You can download it from the following link: https://packetstormsecurity.com/files/download/34044/sthuy_article_openvpn_29940810.B.zip
Source: https://packetstormsecurity.com/files/34044/sthuy_article_openvpn_29940810.B.zip.html