Virtual private network

A virtual private network (VPN) is an overlay network that uses network virtualization to extend a private network across a public network, such as the Internet, via the use of encryption and tunneling protocols. In a VPN, a tunneling protocol is used to transfer network messages from one network host to another.

Host-to-network VPNs are commonly used by organisations to allow off-site users secure access to an office network over the internet. Site-to-site VPNs connect two networks, such as an office network and a datacenter. Provider-provisioned VPNs isolate parts of the provider's own network infrastructure in virtual segments, in ways that make the contents of each segment private with respect to the others. Individuals also use VPNs to encrypt and anonymize their network traffic, with VPN services selling access to their own private networks.

VPNs can enhance usage privacy by making an ISP unable to access the private data exchanged across the VPN. Through encryption, VPNs enhance confidentiality and reduce the risk of successful data sniffing attacks.

A network is a group of communicating computers known as hosts, which communicate data to other hosts via communication protocols, as facilitated by networking hardware. Within a computer network, computers are identified by network addresses, which allow rule-based systems such as Internet Protocol to locate and identify hosts. Hosts may also have hostnames, memorable labels for the host nodes, which are rarely changed after initial assignment. The transmission medium that supports information exchange includes wired media like copper cables, optical fibers, and wireless radio-frequency media. The arrangement of hosts and hardware within a network architecture is known as the network topology.

Apart from physical transmission media, networks comprise network nodes such as network interface controllers, repeaters, hubs, bridges, switches, routers, and modems:

A communication protocol is a set of rules for exchanging information over a network. Communication protocols have various characteristics, such as being connection-oriented or connectionless, or using circuit switching or packet switching.

In a protocol stack, often constructed per the OSI model, communications functions are divided into protocol layers, where each layer leverages the services of the layer below it until the lowest layer controls the hardware that sends information across the media. The use of protocol layering is ubiquitous across the field of computer networking. An important example of a protocol stack is HTTP, the World Wide Web protocol. HTTP runs over TCP over IP, the Internet protocols, which in turn run over IEEE 802.11, the Wi-Fi protocol. This stack is used between a wireless router and a personal computer when accessing the web.

Most modern computer networks use protocols based on packet-mode transmission. A network packet is a formatted unit of data carried by a packet-switched network. Packets consist of two types of data: control information and user data (payload). The control information provides data the network needs to deliver the user data, for example, source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers, with payload data in between.