Overview of Layer 2 Tunneling Protocol
L2TP is a protocol that is used to tunnel PPP over a public network using IP. This protocol allows for the encapsulation of any Layer 3 protocol in its packets because of the fact that the tunneling occurs on Layer 2, thereby making things transparent to Layer 3 and above. Like GRE, L2TP does not provide encryption mechanisms for the traffic it tunnels. Instead, it relies on another protocol such as IPsec or an application layer encryption mechanism to provide that type of security.
The functioning of L2TP is fairly simple, as shown in Figure 12-1. The end device, often a user PC or laptop, establishes a PPP connection to a server known as the LAC (L2TP Access Concentrator) using dialup POTS, DSL, and so ...
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