Using VPNs, an organization can help secure private network traffic over an unsecured network, such as the Internet. VPN helps provide a secure mechanism for encrypting and encapsulating private network traffic and moving it through an intermediate network. Data is encrypted for confidentiality, and packets that might be intercepted on the shared or public network are indecipherable without the correct encryption keys. Data is also encapsulated, or wrapped, with an IP header containing routing information.
VPN service help enable users working at home, on the road, or at a branch office to connect in a secure fashion to a remote corporate server using the Internet. From the users perspective, the VPN is a point-to-point connection between the user's computer and a corporate server. The nature of the intermediate network, the Internet, is irrelevant to the user because it appears as if the data is being sent over a dedicated private link.
There are a number of ways to use VPN. The most common scenario is when a remote user accesses a private network across the Internet using a remote access VPN connection. In another scenario, a remote office connects to the corporate network using either a persistent or an on-demand site-to-site VPN connection (also known as a router-to-router VPN connection).
Each of these VPN scenarios can be deployed to provide connectivity over a public network, such as the Internet, or over a private intranet. VPN connections can also be deployed in an extranet scenario to communicate securely with business partners. An extranet functions as an intranet that can be securely shared with a designated business partner.
With both the remote access and site-to-site connections, VPNs enable an organization to replace long distance dial-up or leased lines with local dial-up or leased lines to an Internet service provider (ISP).