ASN Lookup
Get ASN details, routing prefixes and organization information.
An Autonomous System Number (ASN) identifies a network on the public internet —
every ISP, large enterprise, cloud provider, and CDN has at least one. ASNs are the unit of BGP
routing: when an IP address moves between networks, what changes is which ASN announces it.
Use this tool to look up an ASN's organization, country, and announced IP prefixes; you can also
enter an IP and we'll resolve it to its ASN first.
Running...
Reading the result
- AS number — the numeric identifier (e.g. AS15169 = Google, AS13335 = Cloudflare, AS16509 = Amazon).
- AS name / org — the company that holds the allocation. Names sometimes lag M&A activity by months.
- Country — the country code where the RIR registered the AS, which is not always where the AS operates infrastructure.
- Announced prefixes — the IP blocks this AS is currently advertising to the global routing table. Large carriers can announce thousands of prefixes; a small enterprise typically announces 1–3.
- Type — content, transit, ISP, hosting, or enterprise. Helps you spot whether an IP belongs to a residential ISP or a cloud provider.
Common use cases
- Categorize suspicious IPs in your logs — Cloud / hosting ASNs vs. residential ISPs vs. mobile carriers tell very different stories about a request.
- Trace traffic at the network level — pair with traceroute to see which transit providers a path crosses.
- Identify the real owner of an IP block when the WHOIS data is delegated through intermediaries.
- Verify peering / multi-homing — a network announcing through multiple upstreams.
About ASNs
- 16-bit ASNs (1 – 65534) are mostly exhausted; new ASNs are 32-bit (up to ~4.2 billion).
- Private ASNs (64512 – 65534 and 4200000000 – 4294967294) are valid only inside one organization and don't appear in the global table.
- An AS can announce IPs in many countries; geolocation is per-IP, not per-AS.