What Is an Autonomous System Number (ASN)?

Overview of ASN

An ASN (Autonomous System Number) is a unique identifier that represents a collection of IP prefixes. ASNs are determined and assigned by Regional Internet Registries (RIRs). ASNs play a crucial role in internet routing, organizing IP addresses under a single organization's management structure – these organizations include universities, governments, large organizations, and internet service providers (ISPs).

ASNs can be private or public: public ASNs are used to exchange information over the internet, while private ASNs are used to communicate with individual providers, including those within the same network, or with other networks that owners coordinate with to avoid duplicative ASNs. Both use Border Gateway Protocol (BGP).

Why ASNs Are Important

ASN information empowers companies to trace potential threats back to their source ASN, or analyze market trends by examining network ownership and connectivity. They are also valuable for refining network routing policies that improve speed and reliability.

How to Lookup an ASN Using IPinfo

With IPinfo’s ASN API or database download, users can look up ASN details, including organization names, countries, and related IP prefixes. For businesses concerned with fraud prevention, IPinfo’s ASN data can be used to flag suspicious IP addresses, helping reduce exposure to malicious actors and improve overall cybersecurity posture.

Links to Related Documentation and Tooling

• Hosted Domains by ASNs Report
• ASN API Developer Resource
• IP to ASN Database Developer Resource
• IP Data Types Developer Resource

Additional Resources

• Blog: IPinfo CLI: Lookup IP or ASN details
• Community Post: ASN Explained
• FAQ: Why Some IP Addresses Don't Have ASN Data