Definition: A VPN utilizes public telecommunications networks to conduct private data communications. Most VPN implementations use the Internet as the public infrastructure and a variety of specialized protocols to support private communications through the Internet.
VPN follows a client and server approach. VPN clients authenticate users, encrypt data, and otherwise manage sessions with VPN servers utilizing a technique called tunneling. VPN clients and VPN servers are typically used in these three scenarios:
1. To support remote access to an intranet,
2. To support connections between multiple intranets within the same organization, and
3. To join networks between two organizations, forming an extranet.
The main benefit of a VPN is the lower cost needed to support this technology compared to alternatives like traditional leased lines or remote access servers. VPN servers can also connect directly to other VPN servers. A VPN server-to-server connection extends the intranet or extranet to span multiple networks.