An ASN (autonomous system number) is the number that identifies a network, such as an internet provider, mobile operator, cloud provider or large company, that announces blocks of IP addresses to the rest of the internet.
Networks announce their address blocks with BGP, the internet's routing protocol, so every routed public IP address is announced by at least one autonomous system. The ASN tells you whose network a request came from.
Why does the ASN matter for fraud detection?
The network says a lot about the traffic. An address announced by a hosting provider is probably a server; one from a mobile operator is probably a phone, often behind carrier-grade NAT; one from a university is probably a campus user. ASN data also helps when a single address is new: a fresh server in a hosting network still looks like a server.
It has limits. Large providers run consumer, business and cloud services, and the network's name cannot always tell them apart.
How Hextner uses it
VerifIP's /v1/check returns asn (for example 60729), isp (the network's organisation name) and connection_type, which classifies the network as Data Center, Residential, Mobile, Education, Corporate or Unknown from that name; a datacenter range match wins first. The ASN data comes from MaxMind GeoLite2. /v1/whois adds the registry's record of the network through RDAP. See the field reference and the WHOIS answer.
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