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Autonomous system

(also AS)

Autonomous system definition

An autonomous system is a collection of IP networks and routers under the control of one entity, typically an internet service provider (ISP), a large business, or an educational institution that presents a standard routing policy to the internet. A unique number identifies each AS, the autonomous system number (ASN), used in routing data across the internet.

See also: ISP, BGP

Autonomous system examples

  • Major ISPs: Large internet service providers like AT&T and Comcast each have their own AS.
  • Large businesses: Multinational companies with substantial network infrastructure may have their own AS.
  • Universities: Large educational institutions with significant network needs, like the University of California, Berkeley, might maintain an AS.

Understanding autonomous systems

  • An AS allows for the efficient routing of internet traffic within its network, reducing dependence on external routers.
  • Autonomous systems enable the use of the Border Gateway Protocol (BGP) to exchange routing information between routers in different ASes.
  • Remember that while an AS aids in routing internet traffic, it also plays a part in internet security issues like BGP hijacking.