flow control

A security control mechanism — specifically a set of policies and their enforcement — that governs *where* information is permitted to travel within a system or between interconnected systems, as distinct from *who* is permitted to access it. It "regulates where information can travel within a system and between systems (in contrast to who is allowed to access the information) and without regard to subsequent accesses to that information." Organizations employ flow control policies and enforcement mechanisms to control information movement between designated sources and destinations; enforcement is based on characteristics of the information and/or the information path, and is implemented in boundary protection devices — such as firewalls, gateways, and routers — using rule sets, packet-filtering on header information, or message-filtering on content. In practice it covers a wide range of restrictions: blocking external traffic that claims internal origin, preventing export-controlled data from being transmitted in the clear, restricting web requests to those from an authorized proxy, and limiting inter-organizational transfers based on data structures and content.