Virtual Private Network (VPN) Implementation Options

Virtual Private Network (VPN) Implementation Options
A Virtual Private Network (VPN) is defined loosely as a network in which customer
connectivity among 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 costeffective
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 various 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.
Virtual Private Network Evolution
Initial computer networks were implemented with two major technologies: leased lines for
permanent connectivity and dial-up lines for occasional connectivity requirements. Figure
8-1 shows a typical network from those days.