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Definition: L2TP

(Layer 2 Tunneling Protocol) An IETF protocol that lets remote users access the corporate network. The PPP protocol encapsulates IP packets from the user's devices to the ISP, and L2TP extends that session across the Internet. L2TP was derived from Microsoft's Point-to-Point Tunneling Protocol (PPTP) and Cisco's Layer 2 Forwarding (L2F) technology. See PPP, PPTP and L2F.

L2TP does not include encryption but is often used with IPsec in order to provide virtual private network (VPN) connections. See VPN and VPN protocols.

PPP and L2TP Traffic
The NAS is the control point for remote users. The LAC encapsulates PPP frames with L2TP headers and sends them out as UDP packets. At the other end, the LNS terminates the PPP session and hands the IP packets to the LAN. L2TP can also be run in the user's PC.