An IntroductionUntil recently, reliable communication meant the use of leased lines to maintain a Wide Area Network (WAN). Leased lines, ranging from ISDN (Integrated Services Digital Network, which runs at 144 Kbps) to Optical Carrier-3 (OC3, which runs at 155 Mbps) fiber, provide a business with a way to expand its private network beyond your immediate geographic area. A WAN has clear advantages over a public network such as the Internet in terms of reliability, performance and security, but maintaining a WAN, particularly when using leased lines, can become quite expensive (often costs increase as the distance among offices increases). As the Internet has grown in popularity, businesses have turned to it as a means to extend their networks. First came intranets, sites designed to be used only by company employees. Now, many companies are creating their own virtual private networks (VPNs) to meet the needs of remote employees and distant offices. A typical VPN might have a main local area network (LAN) at a company's corporate headquarters, other LANs in remote offices or facilities, and individual users connecting from 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 connection, such as a leased line, a VPN uses "virtual" connections routed across the Internet from the company's private network to the remote site or employee. What makes a VPN? There are two common types of VPNs:1. Remote Access Also called Virtual Private Dial-up Network (VPDN), this is a user-LAN connection used by a company that has employees who need to connect to the private network from various remote locations. Typically, a company wanting to set up a large remote access VPN provides some form of remote Internet access account to its users using an Internet Service Provider (ISP). The teleworker can then dial a 1-800 number to reach the Internet and use VPN client software to access the company network. A good example of a company that needs a remote access VPN would be a large company with hundreds of field sales people. Remote access VPNs enable secure, encrypted connections between a company's private network and remote users through a third-party service provider.2. Site-to-SiteThrough the use of dedicated equipment and large-scale encryption, a company can connect multiple fixed sites over a public network such as the Internet.