6.2 Dynamic Routing Overview  
  6.2.2 Autonomous systems  
An autonomous system (AS) is a collection of networks under a common administration sharing a common routing strategy. To the outside world, an AS is viewed as a single entity. The AS may be run by one or more operators while presenting a consistent view of routing to the external world.

The American Registry of Internet Numbers (ARIN), a service provider, or an administrator assigns an identifying number to each AS. This autonomous system number is a 16 bit number. Routing protocols, such as Cisco’s IGRP, require assignment of a unique, autonomous system number.

 

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Autonomous System

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