by Richard Bramante

Created on: October 15, 2009

You may be asking the question, what exactly is a Virtual Private Network? In simple terms, it is the ability to create a secure and totally private network between two networks whose only interconnection is the Internet. The next question that would be asked is if the only connection between these two networks is the Internet, which is far from private and fraught with all sorts of hackers, how could you possibly have a Virtual Private Network? This is virtually accomplished using a variety authentication schemes along with strong encryption algorithms to build a secure tunnel through the Internet between the two networks that may be located anywhere on the globe as long as there is access to an Internet connection.

With it being established that it is feasible to create and maintain a secure Virtual Private Network or VPN, what are the basic scenarios for their use? An obvious one is a company environment with one or more branch offices. Before VPN technology was developed, companies would interconnect their branch offices to the main office with dedicated leased lines. These were fixed lines that could not be moved easily if an office needed to move. The cost of these leased lines would have a tariff on them based on the amount of bandwidth that was required between the two offices. These tariffs were billed monthly and costs could rise rapidly with the need for increased bandwidth. The tariff for a leased line is determined not only by the required bandwidth but also by the amount of miles between the remote and main branches of the company. So with the development of VPN technology the need for long, high cost dedicated lines can be eliminated offering increased savings for the company.

A VPN connection between a remote office and the main home office is commonly referred to as a "Branch to Branch" or "Peer to Peer" VPN Tunnel. Each location would require a VPN router to route network traffic from the Local Area Network or LAN over the Internet to the remote office to its peer VPN Router so it can route that traffic onto the LAN it supports. The two VPN routers are configured to know of its peer and that information is used to authenticate the validity of any VPN tunnel that is established between them. The result is that a VPN Router would only accept VPN Internet traffic from a known peer. Any attempts to "hack" through the VPN Router to the LAN it protects would be discarded if it were determined that it is coming from a source that is not its peer.

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