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What is an autonomous system number (ASN)?

Learn what an ASN is and who issues them.

An autonomous system number (ASN) is an identifier that gets issues when an organization registers a new autonomous system (AS). ASNs are assigned worldwide by Regional Internet Registries (RIRs) such as RIPE NCC (Europe), ARIN (North America) and others. ASNs are used to distinguish one AS from another in the BGP routing system.

With the ASN, it is also possible to look up more information about an AS, like with what other ASes they are peering, ect.. A good database to look up this information is PeeringDB.

Examples of Autonomous System Numbers