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Autonomous Systems

An autonomous system (AS) is a set of routers that use the same routing policy while running under a single technical administration. An AS runs interior gateway protocols (IGPs) such as RIP, OSPF, and IS-IS within its boundaries. ASs use exterior gateway protocols (EGPs) to exchange routing information with other ASs. BGP is an EGP.

The outside world views an AS as a single entity, even though it can be a collection of IGPs working together to provide routing within its interior.

Each AS has an identification number provided by an Internet registry or by an Internet service provider (ISP) that uniquely identifies it to the outside world.

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