Prior to the L2TP standard (August 1999), Cisco used Layer 2 Forwarding (L2F) as its proprietary tunneling protocol. L2TP is 100 percent backward-compatible with L2F. L2F is not forward-compatible with L2TP.

L2TP, defined in RFC 2661, is a combination of Cisco L2F and Microsoft Point-to-Point Tunneling Protocol (PPTP). Microsoft supports PPTP in its earlier versions of Windows, and PPTP and L2TP in Windows NT and 2000.

L2TP is used to create a media-independent, multiprotocol virtual private dialup network (VPDN). L2TP allows users to invoke corporate security policies across any VPN or VPDN link as an extension of their internal networks.

L2TP does not provide encryption and can be monitored with a protocol analyzer.

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