Virtual Private Networking Overview
A virtual private network (VPN) is the extension of a private network that encompasses links across shared or public networks like the Internet. A VPN enables you to send data between two computers across a shared or public internetwork in a manner that emulates the properties of a point-to-point private link. The act of configuring and creating a virtual private network is known as virtual private networking.
To emulate a point-to-point link, data is encapsulated, or wrapped, with a header that provides routing information allowing it to traverse the shared or public internetwork to reach its endpoint. To emulate a private link, the data being sent is encrypted for confidentiality. Packets that are intercepted on the shared or public network are indecipherable without the encryption keys. The link in which the private data is encapsulated and encrypted is known as a virtual private network (VPN) connection.
Figure 9.1 illustrates the logical concept of a VPN.
Figure 9.1 Virtual Private Network (VPN)
VPN connections allow users working at home or on the road to obtain a remote access connection to an organization server using the infrastructure provided by a public internetwork such as the Internet. From the user's perspective, the VPN is a point-to-point connection between the computer, the VPN client, and an organization server, the VPN server. The exact infrastructure of the shared or public network is irrelevant because it appears logically as if the data is sent over a dedicated private link.
VPN connections also allow organizations to have routed connections with geographically separate offices or with other organizations over a public internetwork such as the Internet while maintaining secure communications. A routed VPN connection across the Internet logically operates as a dedicated WAN link.
With both the remote access connection and with the routed connection, VPN connections allow an organization to trade in long distance dial-up or leased lines for local dial-up or leased lines to an Internet service provider (ISP).