VPN service providers may offer best-effort performance, or may have a defined service level agreement (SLA) with their VPN customers. Generally, a VPN has a topology more complex than point-to-point.
A virtual private network (vpn) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) as opposed to running across a single private network. The link-layer protocols of the virtual network are said to be tunneled through the larger network. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.
A VPN allows computer users to access a network via an IP address other than the one that actually connects their computer to the Internet.