An overview of the L2F protocol

Julie Cole
Julie Cole | Tech writer and privacy advocate
Last updated: April 20, 2021
An overview of the L2F protocol
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L2F is a Cisco channeling protocol that uses features such as virtual dial-up networks for well-secured data packet transport. L2F is similar in its functionality to the Point-to-Point Tunneling Protocol (PPTP) that was designed by Microsoft.

But before we go further and talk about the L2F protocol, we need to know about VPNs (virtual private networks), which is an exclusive network spread out across an unsecured public network. It enables the users of such VPNs to communicate on public networks securely as if their devices were directly connected to each other.

Software and files that are active on the VPN network will benefit from the services, insurance, and administrative privileges that are available on the private network. The secured connection helps to ensure that sensitive information is safely transmitted from point A to B. It prevents unauthorized people and also hackers from eavesdropping on the traffic, prevents sensitive data from being stolen and allows the user to work remotely.

Virtual Private Network channeling creates a point-to-point connection between two gadgets or devices, often the Virtual Private Network server and your device. Tunneling securely encloses or codes your information into a standard TCP/IP packets and safely transmits it across the Internet.

Because the information is encrypted, unauthorized persons, governments, hackers, and even Internet service providers cannot see or gain control of the information transmission while you are connected to a VPN server. From experience, we have seen people make the mistake of saying that VPN and Proxy services are the same thing and that they can substitute each other.

But this is absolutely not true as when you connect to a proxy server, it becomes a link between your device and the Internet. What this means is that your device’s IP address will be changed to the proxy server’s IP address, making you appear to have come from the proxy server. However, proxy servers do not code your information, so any data that you exchange over the network can be intercepted by hackers, governments and even anybody who is also connected to the server. With VPN comes the assured protection of L2F Protocols.

How does a VPN function?

As a user, you run a VPN client software that supports the Layer 2 forwarding protocol on your device. This software encrypts your information, even before your ISP sees it. The data then goes to the VPN server, and from the VPN server to your online destination. Your destination online sees your connection as coming from the VPN server location, and not from your device and your location.

VPN security protocols

A VPN protocol determines exactly how your information communicates between your device and the VPN server. VPN security protocols have different specifications, giving different benefits to users in a range of circumstances. For example, some security protocols prioritize speed, while others focus more on privacy and security. Let’s take a look at the most common protocols.

These protocols include; Secure Sockets Layer (SSL), Transport Layer Security (TLS), IP security (IPsec), the Point-to-Point Tunneling Protocol, Secure Shell (SSH), and Layer 2 Forwarding, which was later upgraded and named the Layer 2 Tunneling Protocol (L2TP). This was achieved in 1999 when Cisco and Microsoft combined their respective L2F protocol together and created L2TP.

Read more: Most secure VPN protocols

IP Security Protocol

IPsec, as one of the security protocols developed in order to secure data, is often used to secure internet traffic and it works in two modes. Transport mode, which only encrypts the data or information packet message itself, and Tunneling mode, which encrypts the entire data packet. This protocol can also be used in collaboration with other protocols to increase their level of security.

Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocol

SSL and TLS are employed in the security of online retailers and service providers. The mode of operation of these protocols is called the handshake method. In order to know that you are on a secured website and that your transaction is secured, watch out for the “https://” in the address bar. An SSL handshake is performed, which in turn produces the cryptographic framework of the session. This creates a secure connection.

Layer 2 Forwarding protocol

The Layer 2 Forwarding protocol (L2F) is used to establish a secure end-to-end tunnel across a public infrastructure (such as the internet) that connects an Internet Service Provider to an enterprise home gateway.

This tunnel creates a virtual point-to-point connection between the user and the enterprise customer’s network. L2F allows the tunneling of the link layer of higher level protocols.

Right now, Layer 2 Forwarding protocol is not as popular as other protocols, because it has since been upgraded and named Layer 2 Tunneling Protocol, which is somewhat outdated in its own right. L2F does not encrypt data nor code information by itself but relies on the protocol being tunneled to provide privacy.

L2F functions in a way that if there is no current tunnel connection to the desired home gateway from the point of initiation, a tunnel will be initiated:

  • L2F is designed to be largely isolated from the details of the media over which the tunnel is established;
  • L2F needs only that the tunnel provides packet-oriented point-to-point connectivity.

L2F protocol security overview

When the virtual dial-up service is initiated, the ISP pursues authentication only to the extent required to discover the user’s identity (and by implication, their desired Home Gateway). As soon as this is determined, a connection to the Home Gateway is initiated with the authentication information gathered by the ISP. The Home Gateway completes the authentication by either accepting the connection or rejecting it.

The Home Gateway must also protect against attempts by third parties (such as snoopers, hackers) to establish tunnels to the Home Gateway. Tunnel establishment involves an ISP-to-Home Gateway authentication phase to protect against such malicious attacks. Another property that makes L2F protocol more secure is its ability to be used with one or two other security protocols seamlessly.

Final thoughts

In conclusion, Layer 2 Forwarding protocol, is now renamed Layer 2 Tunneling Protocol, since the merger between Microsoft and Cisco in 1999.

It is a vital part of the security features of a VPN because the end to end tunnel it creates alone can keep data encapsulated and transferred safely.

L2F protocol on its own has one limitation that makes it a bit less desirable. And this limitation is that data passed through its tunnel are not encrypted.

If a third party was able to breach the tunnel, they will be able to access the data in the tunnel.

Because of this singular limitation, a secondary protocol like GRE or TCP has to combined with it to encrypt the data. Then integrity of the data will be well secured, giving the authorized users high levels of privacy.

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  1. Big Foot

    Great article! Thank you very much for sharing this awesome post with us.

  2. Katerina Tsikki

    The convenience provided by L2F protocol which tunnels data-link layer frames in protocols such as PPP or SLIP, allowing the creation of VPNs over a public network is just awesome!

  3. emeraldgreen092

    I think IPSec is one of the advanced VPN protocol options the end users have at this point of time as L2F is not secured to be used on its own.

  4. Melissa Brown

    At present, my firm makes use of L2F protocol which is a vital part of the security features of a VPN because the end to end tunnel it creates alone can keep data encapsulated and transferred safely

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