Layer 2 Forwarding

Layer 2 Forwarding (L2F)

Layer 2 Forwarding (L2F) is a tunneling protocol used to support virtual private networks (VPNs) by encapsulating Point-to-Point Protocol (PPP) frames within Internet Protocol (IP) packets. L2F was developed by Cisco Systems as an early VPN solution to enable remote access to corporate networks over the Internet.

Operation

L2F operates by encapsulating PPP frames within IP packets, allowing them to be transmitted over IP-based networks. The L2F protocol involves the following steps:

• Tunnel Establishment: A tunnel is established between the remote client and the L2F server (also known as the L2F Network Server). This tunnel is used to transport PPP frames between the client and the corporate network.
• PPP Session Setup: Once the tunnel is established, the client initiates a PPP session with the L2F server. The L2F server authenticates the client and assigns it an IP address.
• Data Transfer: PPP frames sent by the client are encapsulated within IP packets and transmitted over the Internet to the L2F server. The L2F server decapsulates the PPP frames and forwards them to the corporate network.

Features

L2F provides several features that make it suitable for remote access VPNs:

• Remote Access: L2F allows remote users to access corporate networks securely over the Internet, providing access to resources such as files, applications, and internal services.
• PPP Support: L2F supports the PPP protocol, allowing for authentication, encryption, and compression of data transmitted over the VPN tunnel.
• Scalability: L2F can support a large number of simultaneous VPN connections, making it suitable for enterprise environments.

Advantages

• Compatibility: L2F is compatible with a wide range of networking equipment and software, making it easy to deploy in existing network infrastructures.
• Security: L2F provides encryption and authentication mechanisms to secure VPN connections, protecting data transmitted over the Internet.

Disadvantages

• Complexity: Setting up and configuring L2F tunnels and servers can be complex, requiring knowledge of networking and VPN technologies.
• Overhead: L2F introduces additional overhead due to the encapsulation of PPP frames within IP packets, potentially reducing network performance.

See Also

• Virtual Private Network (VPN)
• Point-to-Point Protocol (PPP)
• IPsec (Internet Protocol Security)
• Layer 2 Tunneling Protocol (L2TP)

References

• RFC 2341 - Cisco Layer Two Forwarding (Protocol) "L2F"