ASN (Autonomous System Number)
An ASN identifies an autonomous system: a network, such as an ISP or hosting company, that announces its own IP ranges to the internet.
What an ASN is
The internet is a collection of independently run networks called autonomous systems. Each one is identified by an Autonomous System Number, written as AS followed by digits, for example AS15169. An autonomous system announces the IP ranges it controls to its neighbors using BGP, and those announcements are how the rest of the internet learns where to send packets for a given address.
An ISP, a cloud provider, a university, a bank, and a content network can each hold one or more ASNs. Small organizations usually do not have one and instead use addresses from their provider.
Why it matters
The ASN tells you who is responsible for an address, and that is a far stronger signal than the city a geolocation database guesses. Websites, payment processors, and fraud systems classify traffic by ASN before anything else:
- A consumer ISP or a mobile carrier is treated as a normal user (residential or mobile IP).
- A hosting, cloud, or VPS network is treated as a server, proxy, or VPN (datacenter IP).
- Networks whose names contain words like "VPN" or "proxy" are flagged outright.
Our anonymity score deducts 25 points for a hosting network and 20 points for a known VPN or proxy network, based on the ASN name and the datacenter list we import.
How we classify networks
We combine the DB-IP Lite ASN database with the public iptoasn.com table to map every announced range to its ASN and name, then apply keyword rules to the name: hosting and cloud words produce hosting, carrier words produce mobile, universities produce education, and so on. The rules are deliberately simple and are shown on the page so you can judge them yourself.
How to check
ASN lookup accepts a number or a name and shows the network's country, type, prefix counts, and a sample of its announced ranges. IP lookup shows the ASN for any single address, and the WHOIS tool fetches the registry record for the ASN via RDAP.
A common misconception
Two addresses in the same ASN do not share a location. A large provider announces ranges in many cities and sometimes several countries; the ASN describes ownership, and geolocation describes use.