AS / ASN Lookup
Look up the autonomous system behind any IP address or ASN — the organisation that actually operates the network, the address blocks it announces, and where it sits in the internet's routing structure.
This is the most reliable identity information an IP address carries. Unlike geolocation, which is an estimate, AS data has to be accurate because global routing depends on it.
What an autonomous system is
The internet is not one network. It is roughly a hundred thousand independently operated networks that agree to carry each other's traffic. Each is an autonomous system with its own number — AS15169 is Google, AS13335 is Cloudflare — and each announces which address blocks it is responsible for.
Those announcements travel by BGP, the protocol that lets every network on the internet learn how to reach every other. When you look up an ASN you are reading the routing system's own record of who owns what.
What the result tells you
- The operator — who actually runs the network, which is often not the brand a customer would recognise.
- Network type — residential ISP, mobile carrier, hosting provider, enterprise or transit backbone. This is what determines how sites treat traffic from the address.
- Announced prefixes — the address blocks the network is responsible for, and therefore its rough size.
- Country of registration — where the organisation registered, which is not necessarily where any given address is used.
Why this is the field to quote in a support ticket
"My connection is slow to your service" is not actionable. "Traffic from AS12345 to your network degrades at the interconnect" is, because it names both networks precisely and tells the engineer where to look.
Peering and transit disputes between networks are a genuine cause of poor performance to one specific destination while everything else is fine. Identifying the two autonomous systems involved is the first step in describing that problem in terms the operators can act on — see the guide to reporting it.
Using it to explain unexpected behaviour
A datacenter or hosting ASN behind an address explains a lot of otherwise puzzling treatment: more CAPTCHAs, blocked signups, rate limiting. Sites use network type as a proxy for automation risk, so traffic from a hosting network is treated with more suspicion than traffic from a residential ISP.
It also identifies VPN and proxy exits, which is the basis of how VPN detection works. If you are checking whether a tunnel is carrying your traffic, watching the ASN change is a stronger signal than watching the IP change.