User Guide

Page 41 SonicWALL Internet Security Appliance User’s Guide
NAT with L2TP Client
L2TP is a standard tunneling protocol that is used to encapsulate Point-to-Point Protocol
(PPP) frames for transmission over TCP/IP, X.25, frame relay, or Asynchronous Transfer
Mode (ATM) networks. It can be used to create virtual private networks (VPN) over public
networks such as the Internet. It also provides interoperability between different VPN
vendors which other protocols do not provide.
PPP provides the connection over which L2TP sends packets through a tunnel. The tunnel
can be initiated by either a dial-up client used by the customer, or by the network access
server (NAS) located at the L2TP service provider such as an ISP. When the client initiates
the connection to the NAS, the NAS is referred to as an L2TP access concentrator (LAC).
The LAC forwards its L2TP traffic to a remote node called an L2TP network server (LNS).
The NAS performs the server-side function of PPP termination and acts as the receiver of
incoming connections. If the NAS initiates the L2TP tunnel to the customer premises, the
client PC acts as the LNS.
A VPN constructed using L2TP can be initiated two ways:
• Client-initiated tunnel - The client initiates a tunnel in a way similar to PPTP tun-
nels.
• NAS-initiated tunnel - If the tunnel is initiated by the NAS, it enables telephone
companies and ISPs to provide corporate customers with VPN solutions.
To configure the SonicWALL for NAT with L2TP Client, follow these steps:
1. Select NAT with L2TP Client from the Network Addressing Mode menu on
the Network tab.
integrated_manual.book Page 41 Friday, October 12, 2001 2:56 PM