A VPDN is a network that extends remote access to a private network using a shared infrastructure. VPDNs use Layer 2 tunnel technologies (L2F, L2TP, and PPTP) to extend the Layer 2 and higher parts of the network connection from a remote user across an ISP network to a private network. VPDNs are a cost effective method of establishing a long distance, point-to-point connection between remote dial users and a private network.
Instead of making connections directly to the network by using the expensive Public Switched Telephone Network (PSTN), access VPDN users only need to use the PSTN to connect to the ISP local point of presence (POP). The ISP then uses the Internet to forward users from the POP to the customer network. Forwarding calls over the Internet as opposed to making a long-distance PSTN call provides dramatic cost saving for the customer.