ASN Lookup
Look up any Autonomous System Number or IP address. Get organisation, IP ranges, country, and routing information.
Autonomous Systems: How the Internet Is Actually Organised
The internet is not one network but tens of thousands of independent ones, each called an autonomous system: a collection of IP prefixes under a single administrative entity with a unified routing policy. Every AS is identified by its Autonomous System Number — AS13335 is Cloudflare, AS15169 is Google, AS16509 is Amazon — assigned by one of the five Regional Internet Registries. When you ask "who owns this IP?", the honest technical answer is "whichever AS announces the prefix that contains it".
Autonomous systems learn how to reach each other through the Border Gateway Protocol. Each AS announces to its neighbours the prefixes it can deliver traffic to, those neighbours pass the announcements on with their own ASN prepended to the path, and every router assembles the result into a global routing table currently approaching a million IPv4 routes. Routing decisions prefer the most specific matching prefix, then the shortest AS path — which is why an ASN lookup against live BGP data tells you who is really originating an address block right now, not just who registered it years ago.
Security teams lean on ASN data constantly. It turns an anonymous IP in a log into an attributable network — "this scan came from a bulletproof hoster in AS-X" is actionable in a way a bare address is not. It separates datacenter, VPN, and cloud traffic from genuine residential connections, which matters for fraud scoring and bot detection. And it powers coarse-grained controls: blocking one abusive ASN covers every prefix it announces, while allowlisting AS15169 keeps Google's crawlers reachable no matter which specific IPs they use this month.
Reading an ASN Lookup Result
ASNThe Autonomous System Number itself, e.g. AS13335. A 16- or 32-bit identifier assigned by a Regional Internet Registry to a single network operator.
OrganisationThe legal entity registered as the holder of the ASN — Cloudflare, Inc. for AS13335, Google LLC for AS15169. Sourced from RIR WHOIS data.
RIRWhich regional registry allocated the ASN: ARIN, RIPE NCC, APNIC, LACNIC, or AFRINIC. A rough signal of where the network is administered.
Announced prefixesThe IP ranges the AS originates in BGP. Large clouds announce hundreds of prefixes; a small regional ISP may announce only one or two.
PeeringThe neighbouring ASNs a network exchanges routes with, at exchanges or via transit. Peering data shows how well-connected a network is and how traffic reaches it.
Well-known ASNsAS13335 (Cloudflare), AS15169 (Google), AS16509 (Amazon AWS), AS8075 (Microsoft) — worth recognising on sight when reading logs or firewall alerts.