IP to ASN Lookup
Find the autonomous system number (ASN) of any IPv4 or IPv6 address. See the AS name, the organization that runs the network, the BGP prefix the address is routed in, and the registry, country, and dates of both.
Input
Protected by Cloudflare Turnstile
Output
Readme
What is an ASN?
The internet is a network of networks. Each independently run network, such as an internet provider, a cloud platform, a CDN, or a university, is an autonomous system (AS) and has an autonomous system number (ASN), for example AS15169 for Google. Autonomous systems use the Border Gateway Protocol (BGP) to announce the blocks of IP addresses (prefixes) they route. The AS that announces the prefix an IP address belongs to is its origin AS, and it tells you which network the address is part of.
Tool description
IP to ASN Lookup finds the autonomous system of an IPv4 or IPv6 address. Enter an IP address, or use your own with the "Use My IP Address" button, to see the ASN, the AS name, and the organization behind it, together with the BGP prefix the address is routed in and where that prefix is registered.
Features
- Works with IPv4 and IPv6 addresses; a full URL with an IP address as its host works too
- Shows the ASN, AS name, and organization of the network that announces the address
- Shows the country, regional internet registry, and registration date of the AS
- Shows the most specific BGP prefix that covers the address, with the country, registry, and allocation date of the prefix
- Lists every origin AS when a prefix is announced by more than one autonomous system (MOAS)
- One-click lookup of your own public IP address
How it works
The tool queries the Team Cymru IP to ASN mapping service over DNS through Google Public DNS:
- Origin lookup: the IP address, written in reverse order, is looked up under
origin.asn.cymru.com(IPv4) ororigin6.asn.cymru.com(IPv6). The answer lists the announced prefixes that cover the address and their origin ASNs. - Most specific prefix: when several prefixes cover the address, for example a /21 and a /24, the longest one is used, because that is the route traffic to the address follows.
- AS details: each origin ASN is looked up under
asn.cymru.comto get the AS name, organization, country, registry, and registration date.
Output explained
| Field | Description |
|---|---|
| ASN | The autonomous system number of the network, e.g. AS15169 |
| AS name | The short handle of the AS, e.g. GOOGLE |
| Organization | The company or institution that holds the AS |
| Country (AS) | The country the AS is registered in |
| Registry | The regional internet registry: AFRINIC, APNIC, ARIN, LACNIC, or RIPE NCC |
| Registered | The date the ASN was assigned |
| BGP prefix | The IP address block announced in BGP that contains the address, e.g. 8.8.8.0/24 |
| Country (network) | The country the prefix is registered in |
| Allocated | The date the registry allocated the address block |
Limitations
- Only public IP addresses can be looked up. Private, loopback, and other reserved addresses are not routed on the internet and have no ASN.
- An address that isn't announced in BGP at the moment has no origin AS, even if its block is registered to an organization.
- The registered country of an AS or prefix is where the holder is registered, not where the server is. Use IP Geolocation Lookup to estimate a server's location.
- The data reflects the global routing table as Team Cymru sees it and can lag behind very recent routing changes.