A Virtual Private Network (VPN) is defined loosely as a network in which customer connectivity amongst multiple sites is deployed on a shared infrastructure with the same access or security policies as a private network. With the recent advent of marketing activities surrounding the term VPNs, from new technologies supporting VPNs to a flurry of VPN-enabled products and services, you might think that the VPN concept is a major technology throughput. However, as is often the case, VPN is a concept that is more than 10-years old and is well known in the service provider market space.
The new technologies and products merely enable more reliable, scalable, and more cost-effective implementation of the same product. With the cost reduction and enhanced scalability associated with new VPN technologies, it's not surprising that VPN services are among the major drivers for Multiprotocol Label Switching (MPLS) deployment in service provider and enterprise networks.
Before discussing a technology (VPN services based on MPLS) designed to solve a problem (cost-effective VPN implementation), it's always advantageous to focus on the problem first, which is what we do in this chapter.
This chapter gives you an overview of VPN services, common VPN terminology, and detailed classification of var0ious VPN usages and topologies that are encountered most often. This chapter also provides an overview of technologies that were used traditionally to implement Virtual Private Networks either on individual service provider backbones or over the public Internet.