L2F, or Layer 2 Forwarding, is a tunneling protocol developed by Cisco Systems, Inc. to establish virtual private network connections over the Internet.
L2F does not provide encryption or confidentiality by itself; It relies on the protocol being tunneled to provide privacy.
L2F was specifically designed to tunnel Point-to-Point Protocol (PPP) traffic.
[1] Virtual dial-up allows many separate and autonomous protocol domains to share common access infrastructure including modems, Access Servers, and ISDN routers.
RFCs prior to 2341 have specified protocols for supporting IP dial-up via SLIP and multiprotocol dial-up via PPP.