Autonomous System

An Autonomous System (usually abbreviated as AS) is a contiguous area of the Internet, i.e. a connected group of routers and physical networks, under a unified administrative control. In a network like the Internet, composed of independent entities which are inter-connected, and cooperate to exchange traffic, formal recognition of the existence of AS's is a necessary step.

AS's are identified with unique Autonomous System numbers (ASNs), which EGPs such as BGP use to identify the entities in a path.