A Planning Framework for Implementing Virtual Private Networks

A virtual private network (VPN) is simply secure network connectivity over a shared public network—basically, a private network on a public network infrastructure (the Internet). Figure 1 (next page) shows an example of a network layer VPN (adapted from Paul Ferguson and Geoff Huston, “What is a VPN? Part I,”The Internet Protocol J., June 1998,pp.2-19).Corporation X’s subnetworks (which belong to a common administrative domain) have established a VPN (depicted by dashed lines) across a portion of the Internet. This VPN is invisible to competitor corporation Y even though it is using common transmission and routing resources. However, deploying a VPN is not so simple; it requires extensive planning because of its large up-front investment in hardware and software, lengthy set-up time, and ongoing maintenance. Here we present a planning framework for organizations based on an actual implementation experience (Samuel Patton, Bryan Smith, and colleagues,“A Virtual Private Network Deployment Framework,” Proc. IEEE Conf. Local Computer Networks, IEEE Press, Piscataway, N.J., 2000, pp. 225-226). Despite the common perception that a VPN is not a customizable solution, a broad spectrum of VPN options is available. Network designers do not anticipate any single VPN solution to supplant others. Instead they forecast that a diversity of choices will continue to emerge, increasing an advanced-planning framework’s value. Until recently, corporations relied primarily on leased transmission capacity or contracted data services from com-