A private network is a network with protected access and secured transmission. It is possible to build such a network using privately owned or leased lines, but is costly to do so. A virtual private network (VPN) is a network that makes use of public telecommunications infrastructure, like the Internet, in order to provide remote individuals or offices with secure access to the network at their central location or headquarters at a markedly reduced cost. Privacy on a virtual private network is maintained through a combination of security procedures and a data transmission system called tunneling or port forwarding. Standards for virtual private networks come from the Internet Engineering Task Force (IETF).
Tunneling is a method of concealing from the public network the fact that data being transmitted over it is part of a private network transmission. There are several ways to approach tunneling. One is called Point-to-Point Tunneling Protocol (PPTP). Developed by Microsoft in conjunction with some other companies, PPTP allows authorized users to access a virtual private network through an Internet service provider (ISP). The generic routing encapsulation system (GRE), which was developed by Cisco Systems, is an alternative tunneling protocol. Tunneling is not considered effective unless used in conjunction with data encryption and decryption.
There are three types of virtual private networks. Trusted VPNs use dedicated circuitry, but transmissions can be compromised when they run through communications switches. The path of a trusted VPN must be set and consistent, with the routing and addressing set prior to its use.
Secure VPNs are those that use encryption between the originating computer or network through to the receiving computer or network. In order to be secure, all traffic on a virtual private network must by both encrypted and authenticated. In addition, the network must be guarded from outside alteration of the security properties.
Combining a secure VPN with a trusted VPN yields a hybrid VPN. Often, only a portion of a trusted VPN is a secure VPN. In this case, it is important that everyone be clear about the boundaries of the secure virtual private network so that considered decisions can be made about sending different types of information across different parts of the network.
Virtual private networks are used by for a variety of purposes. Voice VPNs enable teleconferencing and business meetings with remote participants. Educational institutions may use a VPN to grant faculty members access to campus facilities and resources when they are off-campus, as well as in setting up distance learning programs that students attend remotely.