Autonomous System
Based on RFC 4271, the Autonomous System (AS) refers to a set of routers under a single technical administration. ASes use an interior gateway protocol (IGP) and common metrics to determine how to route packets within the AS, and an inter-AS routing protocol to determine how to route packets to other ASes. Since the introduction of this definition, several IGPs are commonly used for a single AS and several sets of metrics within an AS are sometimes used. The administration of an AS to other ASes still emerges with a single coherent interior routing plan and a consistent picture of the destinations that are reachable through it even when multiple IGPs and metrics are utilized.[1]