VPN encapsulates encrypted data inside another datagram that contains routing information. The connection between two computers establishes a switched connection that is dedicated to the two computers. The encrypted data is encapsulated inside the PPP or IPSec protocols and that connection is used to deliver the data.
A VPN allows anyone with an Internet connection to use the infrastructure of the public network to dial in to the main network and access resources as if he or she were logged on to the network locally. It also allows two networks to be connected to each other securely. Once connected, data can be exchanged between networks. In this way, VPNs create a WAN.
Many elements are involved in establishing a VPN connection, including the following:
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A VPN client The VPN client is the computer that initiates the connection to the VPN server.
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A VPN server The VPN server authenticates connections from VPN clients.
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An access method As mentioned, a VPN is most often established over a public network such as the Internet; however, some VPN implementations use a private intranet. The network that is used must be IP based.
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VPN protocols Protocols are required to establish, manage, and secure the data over the VPN connection. PPTP and L2TP are commonly associated with VPN connections.
VPNs have become very popular because they allow the public Internet to be safely used as a wide area network (WAN) connectivity solution.