Introduction: 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), 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. 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 rticle, you will gain a fundamental understanding of VPNs, and learn about basic VPN components, technologies, tunneling and security. Virtual private networks help distant colleagues work together, much like desktop sharing. A virtual private network (VPN) is a computer network that is implemented in an additional software layer (overlay) on top of an existing larger network for the purpose of creating a private scope of computer communications or providing a secure extension of a private network into an insecure network such as the Internet.
The links between nodes of a virtual private network are formed over logical onnections or virtual circuits between hosts of the larger network. The Link Layer protocols of the virtual network are said to be tunneled through the underlying transport network One common application is to secure communications through the public Internet, but a VPN does not need to have explicit security features such as authentication or traffic encryption.
For example, VPNs can also be used to separate the traffic of different user communities over an underlying network with strong security features, or to provide access to a network via customized or private routing mechanisms. VPNs are often installed by organizations to provide remote access to a secure organizational network. Generally, a VPN has a network topology more complex than a point-to-point connection. VPNs are also used to mask the IP address of individual computers within the Internet in order, for instance, to surf the World Wide Web anonymously or to access location restricted services, such as Internet television.
Remote-Access VPN There are two common types of VPN. Remote-access, also called a virtual private dial-up network (VPDN), is a user-to-LAN connection used by a company that has mployees who need to connect to the private network from various remote locations. Typically, a corporation that wishes to set up a large remote-access VPN will outsource to an enterprise service provider (ESP). The ESP sets up a network access server (NAS) and provides the remote users with desktop client software for their computers. The telecommuters can then dial a toll-free number to reach the NAS and use their VPN client software to access the corporate network.