So what is a good definition of Virtual Private Networking?
Simply defined, a VPN is a virtual network that is kept private by tunneling private data through the underlying infrastructure of a public Internet. VPN technology provides a way of using public network infrastructures, such as the Internet, to provide private, secure access to applications and company resources to employees in remote or home offices, to business partners, and even to customers. A VPN is one or more WAN links over a shared public network, typically over the Internet or an IP backbone from a Network Service Provider (NSP) that simulates the behavior of dedicated WAN links over leased lines. VPN technology uses a combination of tunneling, encryption, authentication, and access control mechanisms and services used to carry traffic over the Internet, a managed IP network or a service providers backbone.
VPN allows the data to be shared between the client and a server, between two servers, or between networks or routers via a public network but it works just like a point-to-point private line. VPN network architecture uses the remote PC (installed with a client software) that makes use of the present telecommunication infrastructure technology like for example phone lines, broadband services, dedicated internet link etc. and a tunneling protocol (incorporated with other authenticated and encrypted protocols) to access the corporate resources like files, emails etc through a VPN server which sits at the perimeter of the corporate network. The diagram that is seen below shows the simple VPN structure between a client and a server:
VPN is a private network that is layered over the public networks for example Internet to connect to the remote sites and remote users with the privacy, security, quality of services with always on connectivity with well manageability features like the leased networks have. A typical VPN structure with remote offices business partners mobile users of the organization connected to the main office through the network services providers point of presence (Pops), looks like the one below shown in the diagram: