The term intranet refers to an organization’s internal computer network, when that network uses Internet Protocol technology to share data, services and systems within the organization. Unlike the Internet, which is a network that provides a connection between separate entities, an intranet is self-contained within a single organization. An intranet can refer to a single internal website, or a more complex and extensive system involving multiple local area networks (LAN).
Any number of well-known Internet Protocols might be in use on any given intranet, including File Transfer Protocol (FTP) for moving and transmitting files, HyperText Transfer Protocol (HTTP) for web services and Simple Mail Transfer Protocol (SMTP) for email services. As such, an intranet functions essentially as a closed and private equivalent of the Internet, providing much of the same functionality while restricting access to a specific set of interrelated users.
Typically, intranets are secured against unauthorized external access through the use of a firewall and gateway. In some cases, often including smaller companies or organizations, an intranet is created simply by employing private IP addresses. In these cases, such an intranet can only be accessed by computers that are a physical part of the local network, although organizations often offer remote access to off-site users through a virtual private network (VPN) that uses encryption and requires user authentication.