HP VPN Firewall Appliances VPN Configuration Guide

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Configuring L2TP
The term "router" in this document refers to both routers and routing-capable firewalls and firewall
modules.
Overview
A virtual private dialup network (VPDN) is a VPN utilizing the dial-up function of public networks such as
ISDN or PSTN networks to provide access services for enterprises, small ISPs, and telecommuters. VPDN
provides an economical and effective point-to-point method for remote users to connect to their home
LANs.
VPDN technology uses a tunneling protocol to build secure VPNs for enterprises across public networks.
Branch offices and traveling staff can remotely access the headquarters' Intranet resources through a
virtual tunnel over public networks. Other users on the public networks are not permitted access.
Main VPDN tunneling protocols are as follows:
• PPTP
• L2F
• L2TP
L2TP includes the benefits of L2F and PPTP and is the most widely used VPDN tunneling protocol.
L2TP (defined in RFC 2661) is a tunneling protocol that transmits PPP frames. It extends the PPP model by
allowing the Layer 2 endpoints that connect to users and PPP endpoints to reside on different devices
interconnected by a packet-switched network, such as Internet.
Typical L2TP networking application
Figure 149 VPDN built by using L2TP
As shown in Figure 149, a VPDN built by using L2TP comprises the following components:
• Remote system—A remote system is usually a remote user's host or a remote branch's routing
device that needs to access the VPDN network.