Overview

A 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.