An IntroductionUntil recently, reliable communication meant using leased lines to maintain a wide area network (WAN). Leased lines, ranging from Integrated Services Digital Network (ISDN, which operates at 144 Kbps) to Carrier-3 fiber optic (OC3, which operates at 155 Mbps), provide a way for a business to expand its private network beyond its immediate geographical area. . A WAN has clear advantages over a public network like the Internet in terms of reliability, performance and security, but maintaining a WAN, especially when using leased lines, can become quite expensive (this cost often increases with the distance between offices). increases).As the popularity of the Internet has grown, businesses have turned to it to expand their own networks. First come intranets, which are sites intended to be used only by company employees. Today, many businesses are creating their own virtual private networks (VPNs) to meet the needs of remote employees and remote offices. A typical VPN may have a primary local area network (LAN) at a company's headquarters, other remote LANs. offices or facilities, and individual users connecting from outside 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 a leased line, a VPN uses "virtual" connections routed over 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 AccessAlso called a virtual private dial-up network (VPDN), this is a user-to-LAN connection used by a company whose employees need to connect to the private network from various remote locations. Typically, a company that wants to set up a large remote access VPN will provide some form of dial-up Internet account to its users through an Internet Service Provider (ISP). The teleworker can then dial a 1-800 number to access the Internet and use their VPN client software to access the company network. A good example of a business needing a remote access VPN would be a large company with hundreds of salespeople in the field. 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 business can connect multiple fixed sites over a public network such as the Internet..