Reading the result
| Field | What it is |
|---|---|
| AS number | The network that announces the address on the internet, as routers see it |
| AS name | The name the network registered, usually a short handle, the organisation and its country |
| Announced prefix | The block that contains the address, as announced in BGP; the most specific one wins |
| Registry | The regional internet registry that allocated the block |
| Prefix allocated | When the registry allocated the block — not when the current holder got it |
| Registry country | The country in the allocation record; not where the address is used |
The AS that announces an address is not always the one that holds it: a hosting provider can announce a customer’s block, and a DDoS protection service announces the blocks it protects. The holder and its abuse contact are in the registration record — a WHOIS lookup of the address shows them.
The five regional registries
| Registry | Region |
|---|---|
| ARIN | United States, Canada, parts of the Caribbean |
| RIPE NCC | Europe, the Middle East and parts of Central Asia |
| APNIC | Asia and the Pacific |
| LACNIC | Latin America and parts of the Caribbean |
| AFRINIC | Africa |
The same lookup from a terminal
Team Cymru answers the same questions over DNS and over its WHOIS service:
dig +short TXT 8.8.8.8.origin.asn.cymru.com # "15169 | 8.8.8.0/24 | US | arin | 2023-12-28"
dig +short TXT AS15169.asn.cymru.com # the AS name
whois -h whois.cymru.com " -v 8.8.8.8"For an IPv4 address the parts are reversed — 1.2.3.4 is asked as 4.3.2.1.origin.asn.cymru.com.
Frequently asked
What is an ASN?
An autonomous system number identifies one network on the internet — a provider, a hosting company, a university, a large company — that decides its own routing. Each AS announces the address blocks it carries to its neighbours over BGP, and that is how traffic for an address finds its way to the right network.
What does the announced prefix mean?
The address block, such as 192.0.2.0/24, that the AS announces and that contains the address you looked up. Routers follow the most specific announcement, so when several cover an address the longest prefix is the one traffic takes; this page lists it first.
Is the country shown where the IP address is?
No. It is the country in the registry's allocation record — usually where the holder is registered — and an address block is often used somewhere else entirely. This page does not guess a location.
Where does the data come from?
From Team Cymru's IP-to-ASN mapping, which combines BGP routing tables collected around the world with the regional internet registries' allocation data, queried over DNS. For the holder's contact details and abuse address, run a WHOIS lookup of the address.
Why are two AS numbers shown for one address?
Sometimes more than one AS announces the same prefix — during a migration, for anycast services, or because of a misconfiguration. Each announcement is listed.