3 Components of a network security system
3.4 Virtual Private Network (VPN)

VPN stands for "Virtual Private Network". A Virtual Private Network (VPN) is a network technology that makes it possible to use a public network such as the Internet for private communication by creating a secure (encrypted) network connection.

VPNs are often used to enable remote users to securely connect to a private network, and in this way, to extend intranets worldwide. In other words, a VPN enables sending data between two computers using the routing infrastructure provided by a shared or public internetwork (such as the Internet) in a manner that emulates the properties of a point-to-point private link. The secure connection appears to the user as a private network communication, despite the fact that this communication occurs over a public internetwork, hence the name virtual private network.

There are several motivations for building VPNs, but a common thread is that they all share the requirement to "virtualize" some portion of an organization's communications—in other words, make some portion (or perhaps all) the communications essentially "invisible" to external observers, while taking advantage of the efficiencies of a common communications infrastructure. The common uses of VPNs are: secure remote access to corporate resources over Internet and connecting networks over Internet. A VPN solution should provide the following security services: