Securing Windows Server 2003

Virtual Private Networks

Virtual private networks, or VPNs, allow you to use public networks, such as the Internet, as your own private, secure network connection. Many companies use VPNs to connect branch offices to headquarters via the Internet. VPNs rely on data encapsulation and encryption to work and provide reliable, secure connectivity options for remote access.

Operating Theory

Understanding how a VPN works requires you to first understand the basic nature of modern networking. Networks use layered protocols, called stacks, to perform various functions. Users interact most directly with the application layer, which is located at the top of the network stack. A web browser, for example, uses the application-level protocol HTTP.

The collection of wires and electrical signals that form a network exists at the bottom layer of the stack. In between the high- and low-level protocols are midlevel protocols that package data for delivery to specific machines and make sure the data arrives safely at its destination.

When your web browser transmits an HTTP request, your computer’s IP stack packages, or encapsulates, that request in a packet that uses the TCP protocol. The TCP packet is then encapsulated within a lower-level IP packet, then again within an Ethernet packet. The Ethernet packet contains the information necessary for the data to be translated into electrical signals and placed onto the network. The IP and TCP protocols contain information necessary for routers to get the ...