Air gap (networking)

An air gap, air wall, air gapping or disconnected network is a network security measure employed on one or more computers to ensure that a secure computer network is physically isolated from unsecured networks, such as the public Internet or an unsecured local area network. It means a computer or network has no network interface controllers connected to other networks, with a physical or conceptual air gap, analogous to the air gap used in plumbing to maintain water quality. An air-gapped computer or network is one that has no network interfaces, either wired or wireless, connected to outside networks. Many computers, even when they are not plugged into a wired network, have a wireless network interface controller (WiFi) and are connected to nearby wireless networks to access the Internet and update software. This represents a security vulnerability, so air-gapped computers either have their wireless interface controller permanently disabled or physically removed. To move data between the outside world and the air-gapped system, it is necessary to write data to a physical medium such as a thumbdrive, and physically move it between computers. Physical access has to be controlled (man identity and storage media itself). It is easier to control than a direct full network interface, which can be attacked from the exterior insecure system and, if malware infects the secure system, can be used to export secure data. That's why some new hardware technologies are also available like unidirectional data diodes or bidirectional diodes (also called electronic airgaps), that physically separate the network and transportation layers and copy and filter the application data. In environments where networks or devices are rated to handle different levels of classified information, the two disconnected devices or networks are referred to as low side and high side, low being unclassified and high referring to classified, or classified at a higher level. This is also occasionally referred to as red (classified) and black (unclassified).