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How Virtual Private Networks Work
by Jeff Tyson

 › Introduction to How Virtual Private Networks Work
What Makes A VPN?
Analogy: Each LAN is an Island
VPN Security
VPN Technologies
Lots More Information

Special thanks to Cisco Systems, Inc., for its support in creating this article.
The world has changed a lot in the last couple of decades. Instead of simply dealing with local or regional concerns, many businesses now have to think about global markets and logistics. Many companies have facilities spread out across the country or around the world, and there is one thing that all of them need: A way to maintain fast, secure and reliable communications wherever their offices are.

Until fairly recently, this has meant the use of leased lines to maintain a wide area network (WAN). Leased lines, ranging from ISDN (integrated services digital network, 128 Kbps) to OC3 (Optical Carrier-3, 155 Mbps) fiber, provided a company with a way to expand its private network beyond its immediate geographic area. A WAN had obvious advantages over a public network like the Internet when it came to reliability, performance and security. But maintaining a WAN, particularly when using leased lines, can become quite expensive and often rises in cost as the distance between the offices increases.

As the popularity of the Internet grew, businesses turned to it as a means of extending their own networks. First came intranets, which are password-protected sites designed for use only by company employees. Now, many companies are creating their own VPN (virtual private network) to accommodate the needs of remote employees and distant offices.

Image courtesy Cisco Systems, Inc.
A typical VPN might have a main LAN at the corporate headquarters of a company, other LANs at remote offices or facilities and individual users connecting from out in the field.

Basically, a VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together. Instead of using a dedicated, real-world connection such as leased line, a VPN uses "virtual" connections routed through the Internet from the company's private network to the remote site or employee. In this edition of HowStuffWorks, you will gain a fundamental understanding of VPNs, and learn about basic VPN components, technologies, tunneling and security.

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Table of Contents:
› Introduction to How Virtual Private Networks Work
What Makes A VPN?
Analogy: Each LAN is an Island
VPN Security
VPN Technologies
Lots More Information


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