L2TP Layer Two Tunnelling Protocol
L2TP has been defined using the best features of PPTP (Point to Point Tunnelling Protocol) and L2F (Layer 2 Forwarding). It has the ability to encapsulate PPP frames so they can be sent over IP , X.25, Frame Relay , or ATM (Asynchronous Transfer Mode) networks. When using L2TP on an IP based network, the IP datagram supporting the L2TP payload employs the services of UDP (User Datagram Protocol).
