What is Layer 2 Forwarding (L2F), and How It Works?

Ali Qamar  - Cybersecurity Analyst
Last updated: November 6, 2023
Read time: 6 minutes
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The Layer 2 Forwarding protocol is a media-independent technology developed at Cisco Systems. It came to life at the first Virtual Private Networks development stages. Discover how it works, its advantages and disadvantages, and more in this guide.

The Cisco System’s L2F (Layer 2 Forwarding protocol) is a must-have tunneling protocol for every VPN service. It creates an end-to-end encrypted tunnel for secured data traffic around the internet. It primarily facilitates the tunneling of data-link frames in PPP (Point-to-Point Protocol) or SLIP (Serial Line Internet Protocol) web protocols. This way, it establishes a virtual private network over the internet. However, L2F lacks data encryption, becoming less secure than the other protocols.

The Layer 2 Forwarding (L2F) protocol is a media-independent technology developed at Cisco Systems. It’s a media-independent tunneling protocol that came to life at the first Virtual Private Networks development stages. It allows for VPNs to exist over a public network (such as the Internet) by turning data-link layer packets into web protocols like SLIP (Serial Line Internet Protocol) or PPP (Point-to-Point Protocol).

Servers can use L2F for things such as user authentication through dynamic address allocation, Remote Authentication Dial-In User Service (RADIUS), and Quality of Service (QoS). Cisco’s Internetwork operating system implements L2F in routers as well.

The tunneling approach to creating private networks is independent of the Internet Protocol (IP). Hence, the same technology can create secure tunnels in other network contexts like ATMs or Frame Relay.

The L2F protocol: How does it work?

Let’s take the PPP protocol. It connects a dial-up client with the NAS (short form of network access server) when it receives the call using Layer 2 Forwarding (L2F).