Advantages and Disadvantages of L2TP

Layer 2 Tunneling Protocol (L2TP) is a combination of the earlier Microsoft Point-to-Point Tunneling Protocol (PPTP) and Cisco System’s Layer 2 Forwarding. Rather than having competing protocols for tunneling, the Internet Engineering Task Force (IETF) asked the two companies to work together to combine their protocols. L2TP is the result.

At its heart L2TP incorporates all the features of PPTP but runs over a faster transport protocol (UDP) and uses IPSec for encryption. The start-point of an L2TP tunnel is known as the L2TP Access Concentrator (LAC) while the end-point is called the L2TP Network Server (LNS). The LAC is the initiator of the tunnel while the LNS is the server, which waits for new tunnels. When it is established traffic through the tunnel is bi-directional.

L2TP: the advantages

As L2TP incorporates IPSec for security it has advantages over PPTP in that data is much more secure. In addition L2TP prevents data from being altered while moving between the sender and receiver. It also encrypts the authentication process making it more difficult for someone to listen in the transmission. As it uses UDP to encapsulate data, L2TP is also faster and easier to configure with most firewalls. If security is more important to your VPN than speed then L2TP is the recommended protocol.

L2TP: the disadvantages

With some firewalls, however, L2TP is at a disadvantage as it encapsulates the data twice, which can affect the speed of a transmission. L2TP also takes a lot to configure including computer certificates. On Microsoft Server 2008 changes to the registry may also need to be made before L2TP can be used. One of the most common causes of an L2TP failure is a mismatch between security keys. Since L2TP uses pre-shared keys, if a key is changed it must be changed at both ends of the tunnel. L2TP will not work with Network Address Translation (NAT) without a NAT-T client and a NAT-T VPN.

L2TP encryption also involves higher CPU usage, so if speed is more important than security on your VPN, using PPTP alone is a better solution.

You can easily compare advantages and disadvantages of L2TP and other VPN protocols here.