L2F, or Layer 2 Forwarding, is a network tunneling protocol developed by Cisco Systems. Its primary purpose is to enable the creation of Virtual Private Networks (VPNs) by tunneling data-link layer frames—such as those from Point-to-Point Protocol (PPP) or Serial Line Internet Protocol (SLIP)—over public or private networks, most commonly the Internet.
L2F functions at the Data Link Layer (Layer 2) of the OSI model, encapsulating data frames for transmission across IP networks. It establishes a tunnel between a remote user’s network and a central site (such as a corporate network), making it appear as if the remote user is directly connected to the private network. L2F was specifically designed to tunnel PPP traffic, allowing ISPs or network access servers (NAS) to forward PPP frames from clients to remote nodes (often called “home gateways”). L2F is not tied to IP and can also operate over other network types, such as Frame Relay or ATM.