Corporations have traditionally leased transmission capacity or contracted bandwidth services from common carriers to create their own private wide area network (WAN). However, a WAN is expensive to create and maintain. The economics and technology justifying a WAN drastically changed in the 1990s due to the following factors:

• Decreasing costs for Internet connectivity;
• Increasingly higher bandwidth connections to the Internet; and
• Mature encryption technology for secure Internet communications.

These changes made feasible a new type of network called a Virtual Private Network (VPN) which provides all the features of a private WAN for a fraction of the cost.

A Virtual Private Network is simply a secure system of connectivity over a public network—a private network on a public network infrastructure (the Internet). A VPN is "virtual" in the sense that it has no corresponding physical network but rather shares physical circuits with other...