ASN Lookup.
Find out which network an IP address belongs to, or look up any AS number: its name, owner, announced prefix, registry details and abuse contact.
100% free, no sign-up. To stop automated scanning, each browser can run up to 10 scans per tool every 3 hours; only that count is kept (privacy).
What Is an ASN Lookup?
An autonomous system (AS) is a network, or group of networks, run by one organisation with a single routing policy on the internet. Internet providers, hosting companies, universities and large businesses each run one. Every AS has a unique number, its ASN, for example AS15169 for Google and AS13335 for Cloudflare.
Networks use their ASN to announce which IP addresses they hold and to swap traffic with other networks through BGP, the routing protocol of the internet. When you look up an IP address, the AS that announces it tells you which network really carries its traffic. That can differ from the organisation that owns the address block.
This tool takes an AS number, an IP address or a domain name. It reads the AS name from public routing data and the registry record from the regional internet registry. For the full record of an address block, use the IP WHOIS lookup.
The Network Behind an Address.
The AS name and prefix come from public routing data, and the registry record from the regional internet registry that allocated the number.
AS number and name
The autonomous system number and the name its owner gave it, such as AS15169, GOOGLE.
Owner organisation
The company or institution the registry lists as the holder of the AS number.
Announced prefix
When you search by IP or domain, the address block the AS announces for that address, such as 8.8.8.0/24.
Registry and dates
Which regional registry (ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC) allocated it, and when it was registered and last changed.
Abuse contact
The abuse mailbox of the network, for reports of spam, attacks or other misuse.
Any starting point
Type an AS number, an IP address (IPv4 or IPv6) or a domain name. The tool finds the AS for you.
Common Problems and Fixes.
What to do with an AS number.
I only have an IP address
Type the IP address. The tool finds the AS that announces it and shows the prefix, so you do not need to know the number first.
The AS is a CDN or a big cloud
Sites behind a content delivery network or large cloud platform show that company's AS, not the small host or the site owner. The real server is hidden behind it.
The owner differs from the IP WHOIS owner
The AS is who announces the address. The address block can be owned by one company and announced by another, for example when it is leased or hosted.
It says the AS has no public record
The number may not be allocated, may be private (64512 to 65534 and 4200000000 and above), or may not be announced. Check the digits and try again.
I want every prefix an AS announces
This tool shows the prefix for the address you give. For a full list of announcements, use a BGP looking glass or your provider's network team.
I need to report abuse from a network
Copy the abuse contact from the registry record and send your evidence with times, time zone and log lines.
Related Free Tools.
Frequently Asked Questions
Quick answers about this tool.
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