Microsoft® Windows Server 2003: Administrator’s Companion

Virtual Private Networks

Before you explore virtual private networks (VPNs), what they mean, and why they’re useful, take a second to consider that acronym, VPN: “virtual,” as in simulated; “private,” as in secret and confidential; “network,” as in a collection of computers.

Logically, a VPN is simply an extension of a private network. In reality, private networks are geographically isolated from remote users and other private networks by nonsecure communication lines such as the Internet. When you use a secure, network-level protocol like IPSec, a private link can be emulated between two separate networks. Both requestor and authenticator perceive what is actually the wrapping of data before it passes through nonsecure extranets or intranets ...