This document defines and compares different types of VPN technologies. It explains that a VPN uses encryption and tunnels to securely transfer private network traffic over a public network like the Internet. The main VPN protocols discussed are PPTP, L2TP, and IPsec. PPTP is a Microsoft-developed protocol that ensures messages between VPN nodes are secure. L2TP combines features of PPTP and L2F protocols. IPsec supports two encryption modes and uses ISAKMP/Oakley for authentication using public keys. Site-to-site and remote access VPNs allow connections between networks and remote computers/devices over the Internet.