Free ASN lookup. Enter an IP address or a domain and see the Autonomous System that announces it: the AS number, the organisation name, the BGP prefix, the country, and the regional registry. Domains are resolved to their addresses first. Data comes live from Team Cymru's global routing view via our London probe. The fast way to answer "who runs this IP" and to identify the network behind a host.
An Autonomous System is a block of the internet under a single routing policy, run by one operator, an ISP, a hosting company, a cloud provider, or a large enterprise. Each one has an AS number (for example AS15169 for Google). When you map an IP to its ASN, you learn which network actually announces that address to the rest of the internet, along with the BGP prefix it falls in and the regional registry that allocated it. It is the most reliable way to answer "who runs this IP".
City-level geolocation is a best-effort guess and is often wrong for cloud and CDN addresses. The ASN is not a guess: it comes straight from the global routing table, so it reliably identifies the operator behind an address even when the city is unknown. That makes ASN lookup the better tool for identifying a hosting provider, spotting a CDN, or attributing traffic and abuse to a network.
An Autonomous System Number identifies a network that operates under a single routing policy and announces its own IP ranges to the internet via BGP. Every major ISP, cloud, and CDN has one or more.
Enter an IP address or a domain in the tool above. A domain is resolved to its addresses first, then each is mapped to its origin AS number, organisation, and BGP prefix.
A BGP prefix is the block of IP addresses (such as 8.8.8.0/24) that an Autonomous System announces to the internet. It is the unit of routing, and it tells you the size and boundary of the range an address belongs to.
Geolocation estimates a physical location for an IP and is often imprecise. The ASN identifies the network operator behind the IP from the routing table, which is far more reliable, especially for cloud and CDN addresses.
