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What Is an ASN?
ASN stands for Autonomous System Number. It is the identifier used to represent a network or routing domain in interdomain routing on the Internet.
In practice, ASNs are used with BGP, the Border Gateway Protocol. An organization that operates an ASN can announce IP prefixes, exchange routing information with other networks, and define how traffic should move between peers, providers, and customers.
You can think of an autonomous system as a network under a single routing policy. The ASN is the number that other networks use to identify that system when routes are advertised and propagated across the Internet.
ASNs matter because they help explain who is originating a route, how a prefix is connected to the rest of the Internet, and how network relationships influence path selection. They are a basic building block for routing analysis, peering, and operational troubleshooting.