What is a Virtual Private Network?

A virtual private network (VPN) extends a private network across a public network, and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. Applications running across a VPN may therefore benefit from the functionality, security, and management of the private network.

VPN technology was developed to allow remote users and branch offices to access corporate applications and resources. To ensure security, the private network connection is established using an encrypted layered tunneling protocol and VPN users use authentication methods, including passwords or certificates, to gain access to the VPN. In other applications, Internet users may secure their transactions with a VPN, to circumvent geo-restrictions and censorship, or to connect to proxy serversto protect personal identity and location to stay anonymous on the Internet. However, some Internet sites block access to known VPN technology to prevent the circumvention of their georestrictions, and many VPN providers have been developing strategies to get around these roadblocks.

A VPN is created by establishing a virtual point-to-point connection through the use of dedicated connections, virtual tunneling protocols, or traffic encryption. A VPN available from the public Internet can provide some of the benefits of a wide area network (WAN). From a user perspective, the resources available within the private network can be accessed remotely.

Types of VPNs

Early data networks allowed VPN-style connections to remote sites through dial-up modem or through leased line connections utilizing Frame Relay and Asynchronous Transfer Mode (ATM) virtual circuits, provided through networks owned and operated by telecommunication carriers. These networks are not considered true VPNs because they passively secure the data being transmitted by the creation of logical data streams. They have been replaced by VPNs based on IP and IP/Multi-protocol Label Switching (MPLS) Networks, due to significant cost-reductions and increased bandwidth provided by new technologies such as digital subscriber line (DSL) and fiber-optic networks.

VPNs can be either remote-access (connecting a computer to a network) or site-to-site (connecting two networks). In a corporate setting, remote-access VPNs allow employees to access their company’s intranet from home or while traveling outside the office, and site-to-site VPNs allow employees in geographically disparate offices to share one cohesive virtual network. A VPN can also be used to interconnect two similar networks over a dissimilar middle network; for example, two IPv6 networks over an IPv4 network.

VPN systems may be classified by:

  • the tunneling protocol used to tunnel the traffic
  • the tunnel’s termination point location, e.g., on the customer edge or network-provider edge
  • the type of topology of connections, such as site-to-site or network-to-network
  • the levels of security provided the OSI layer they present to the connecting network, such as Layer 2 circuits or Layer 3 network connectivity
  • the number of simultaneous connections.

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