ASN Lookup

ASN Lookup: Which Network Announces an IP Address

Enter an IPv4 or IPv6 address and this tool finds the autonomous system (AS) that announces it on the internet, the exact range it falls in, and that network's name and registration country. Enter an AS number instead (AS13335 or just 13335) to see what the network announces: number of prefixes, total IPv4 addresses, IPv6 space, its rank by size worldwide and in its country, and the first 25 prefixes.

The answer comes from a daily snapshot of the global BGP routing table published by iptoasn.com, so lookups are instant and do not contact the address you enter. Only public addresses can be looked up; private, loopback, CGNAT and other reserved ranges are refused.

How to Read the Results

• Matching range: the announced block that contains your address, as a start and end address and as CIDR. Neighbouring prefixes from the same network are merged in the source data, so the range can be larger than a single BGP route.
• Name: the AS handle and organisation as registered, for example CLOUDFLARENET - Cloudflare, Inc.
• Country: where the network is registered with its regional registry. It is not a geolocation of the address; a CDN registered in the US serves users worldwide.
• IPv4 / IPv6: how many prefixes the AS announces and how much address space they cover. IPv6 is given in /48 and /32 blocks.
• Rank: position among all networks by announced IPv4 space, worldwide and in the registration country.

Common Questions

• "Not announced": no network currently routes that address. It may be unallocated, held in reserve by its owner, or only used internally.
• The owner looks wrong: BGP shows who routes an address, which can differ from the registry holder. Cloud customers, leased blocks and DDoS-protection services all announce space registered to someone else. Use IP WHOIS for the registration record.
• Private ASNs: AS64512 to AS65534 and AS4200000000 and up are for private use. Seeing one announce public space usually means a route leak.

Every network also has a page in the ASN directory, and networks by country compares address space between countries.