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AS, Autonomous System
AS, Autonomous System
The purpose of an autonomous system is to provide a standard routing policy from a network to the internet. According to an older definition, an ISP (Internet Service Provider) with independent connections to multiple networks fit under this description. The definition was modified because multiple networks and organizations now have the ability run BGP (Border Gateway Protocol) using an ISP’s AS number to establish internet connections. This is made possible because an ISP is required to have a publicly registered autonomous number.
A unique AS number is designated to each autonomous system for the use of BGP routing. AS numbers are very essential in BGP because they specifically identify each individual network on the web. The IANA (Internet Assigned Numbers Authority) has reserved autonomous system numbers 64512 through 65534 so that they may be used only for private purposes. All AS numbers reserved by the IANA should never be used in an active environment.