What is an ASN (autonomous system number)?
An ASN identifies the network that announces an IP address on the internet. Learn how ASNs work and why they matter for proxies, security and troubleshooting.
Networks of networks
The internet is made of tens of thousands of independently operated networks. Each one that exchanges routes with others using BGP is an autonomous system (AS), and each is identified by a number: its ASN.
Examples: AS15169 is Google, AS7922 is Comcast, AS16509 is Amazon Web Services. When your IP is looked up, the ASN tells you which organisation announces the block your address belongs to.
Why the ASN matters
The ASN is one of the most reliable pieces of IP intelligence because it comes from public routing data rather than guesswork. It is the fastest way to tell whether an address belongs to a consumer ISP, a mobile carrier, a university, or a cloud provider.
Fraud and bot-detection systems use it heavily: traffic from a hosting ASN claiming to be a home user is a classic mismatch. Proxy buyers use it to confirm they received the network they paid for.
ASN vs ISP
They often coincide, but not always. A regional ISP may buy connectivity from a larger carrier, and some address blocks are announced by a different organisation than the one that serves the end customer. Treat the ASN as the routing owner and the ISP as the service provider.