A computer network is composed of multiple computers connected together using a telecommunication system for the purpose of sharing data, resources and communication. For instance, a home computer network may consist of two or more computers that share files and a printer using the network. The size and scalability of any computer network are determined by the hardware used as well as which protocols are being implemented.

Local Area Network (LAN)

A network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. The defining characteristics of LANs, in contrast to WANs (wide area networks), include their much higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines.

Switches

Switches are the device of networking that directs traffic to the correct node by filtering and forwarding packets between Nodes. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs. In a circuit-switched data network, a switch is used to create a virtual circut between the pairs of endpoints. This means that it creates a path to the destination node from the source node.

Routers

Routers are the networking device that forwards data packets along networks by using headers and forwarding tables to determine the best path to forward the packets. Routers also provide interconnectivity between like and unlike devices on the network. This is accomplished by examining the Header of a data packet. They use protocols such as ICMP to communicate with each other and configure the best route between any two hosts. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Routers are usually located at gateways, the places where two or more networks connect. Many household DSL and Cable Modems are also routers.

A virtual private network is a communications network tunneled through another network, and dedicated for a specific 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 out the traffic of different user communities over an underlying network with strong security features.

A VPN may have best-effort performance, or may have a defined Service Level Agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point. The distinguishing characteristic of VPNs are not security or performance, but that they overlay other network(s) to provide a certain functionality that is meaningful to a user community.