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User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform
Chapter 2
Configuration of L2TP
2-1
Chapter 2 Configuration of L2TP
2.1 Brief Introduction to L2TP Protocol
2.1.1 Overview of VPDN
I. Brief induction to VPDN
In VPDN, VPN is fulfilled with dial-up and access services (ISDN PSTN) of public
network, which provides access service for enterprises, mini ISP and mobile offices. As
telecom carriers and large ISPs have a lot of access equipment, facilities and
management experiences, other enterprises can make full use of their existing
equipment and facilities instead their own investment on access equipment, so that
their services can be more specialized and systematic.
VPDN adopts private network encryption and communication protocol, so enterprises
can establish safe VPN on public networks. Enterprise personnel on business leave
can connect with enterprise's remote internal network via virtual encryption channel,
while other users on public networks can not access the Intranet resources via such
virtual channel.
VPDN is often used by the following users:
z Those users whose branches are geographically distributed, with many mobile
personnel, e.g. enterprise users and tele-education users.
z Those users whose are geographically distributed have to rely on toll calls or even
international toll calls.
z Those who have specific requirements for line security and availability.
II. Operation principle of VPDN
The networking diagram of typical VPDN application is shown in the following figure.
PC
PSTN/ISDN
Remote users
NAS
Remote users
Internal server
Internet backbone network
L2TP
NAS
LNS
Figure VPN-2-1 Networking diagram of typical VPDN application
VDPN is composed of NAS, equipment at user side and management tool.