Most VPN systems use one of two main protocols: Point-to-Point Tunneling Protocol (PPTP) or IP Security (IPSec). IPSec is the more widely used protocol for VPNs. Other VPN systems use varying degrees of both protocols. Additionally, Microsoft and Cisco jointly developed another VPN protocol called Layer Two Tunneling Protocol (L2TP).
Point-to-Point Tunneling Protocol was originally designed and developed by a consortium of companies to encapsulate non-TCP/IP protocols such as IPX over the Internet using Generic Routing Encapsulation (GRE). Security in the protocol was added later.
GENERIC ROUTING ENCAPSULATION
Many protocols are currently available that are designed to encapsulate or hide one protocol in another, normally ...