Find out which network operates an IP address, or look up any autonomous system number directly. You get the AS name, organization, country, regional registry, abuse contact and the IPv4 and IPv6 prefixes it announces on the internet.
Last updated:
Enter an AS number such as AS15169 or an IP address and click Look up ASN to see who operates the network.
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How to use the ASN Lookup
Enter an AS number such as AS13335, an IP address such as 8.8.8.8, or a domain name.
Click Look up ASN or press Enter.
Read the summary: the AS number, its operator, country, registry and number of announced prefixes.
For IPs, check which prefix and origin AS cover the address.
Scroll to the prefix table or download it as CSV, and use the abuse contact to report misuse.
Reserved and special AS numbers
Range
Purpose
Defined in
AS0
Reserved; marks address space that must not be routed
RFC 7607
AS1 – AS64495
Public 2-byte ASNs assigned by the registries
IANA
AS23456
AS_TRANS, stands in for 4-byte ASNs on old routers
RFC 6793
AS64496 – AS64511
Documentation and examples
RFC 5398
AS64512 – AS65534
Private use (2-byte)
RFC 6996
AS65535
Reserved
RFC 7300
AS65536 – AS65551
Documentation (4-byte)
RFC 5398
AS131072 – AS4199999999
Public 4-byte ASNs
IANA
AS4200000000 – AS4294967294
Private use (4-byte)
RFC 6996
The five regional internet registries
IANA hands out blocks of AS numbers and IP addresses to five regional internet registries (RIRs), which assign them to networks in their region. The registry shown in the result is where the AS is registered, which usually but not always matches where the network operates.
Registry
Region
ARIN
United States, Canada, parts of the Caribbean
RIPE NCC
Europe, the Middle East and Central Asia
APNIC
Asia-Pacific
LACNIC
Latin America and parts of the Caribbean
AFRINIC
Africa
Practical uses
Abuse reports: find the network that routes a spamming or attacking IP and contact its abuse address.
Firewall rules: download an AS's prefix list to allow or block a provider's ranges, and expand ranges with the CIDR to IP Range tool.
Troubleshooting: check whether a site is served from a CDN or a particular cloud, and compare with reverse DNS and IP geolocation.
Frequently asked questions
What is an ASN?
An Autonomous System Number identifies a network that runs its own routing policy on the internet, such as an ISP, a cloud provider, a university or a large company. Networks exchange routes with each other using BGP, and every route carries the ASN of the network that originates it. There are about 120,000 ASNs in use today.
How do I find the ASN of an IP address?
Enter the IP address. The tool finds the most specific BGP prefix that currently covers it and the AS that announces that prefix, using Team Cymru's public IP-to-ASN mapping queried over DNS-over-HTTPS. It then loads the AS details from the regional registry.
What is the difference between 2-byte and 4-byte ASNs?
Originally AS numbers were 16-bit (1 to 65535). Since RFC 4893 (now RFC 6793) they are 32-bit, allowing over 4 billion. Numbers above 65535 are 4-byte ASNs and can also be written in asdot notation, for example 4200000000 is 64086.59904. Old routers that do not understand them see AS23456 instead.
What are private ASNs?
AS64512 to 65534 and AS4200000000 to 4294967294 are reserved for private use (RFC 6996), similar to private IP ranges. Companies use them inside their networks or for BGP sessions with their provider, and they must be removed before routes are announced to the internet.
Why does an IP show a different company than I expected?
The ASN shows who routes the address, which is often a hosting or cloud provider, a CDN or an ISP rather than the website owner. A site behind Cloudflare, for example, shows AS13335. To see who registered the IP range itself, use the WHOIS Lookup.
Where does the data come from?
IP-to-ASN mapping and AS names come from Team Cymru's public DNS service, queried via Cloudflare or Google DNS-over-HTTPS. Registration details come from the regional internet registries' RDAP servers through rdap.org, and announced prefixes from the RIPE NCC's RIPEstat API. All requests go directly from your browser.
How current are the announced prefixes?
RIPEstat builds the list from BGP data collected by its route collectors around the world and updates it several times a day. A prefix announced or withdrawn in the last few hours may not appear yet.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.