ASN Lookup
Find the Autonomous System Number behind any IP address.
Free IP to ASN lookup for any IPv4 or IPv6 address. This AS number lookup returns the autonomous system, the organization operating it, and the announced network prefix — the networking data you need to tell a residential ISP apart from a datacenter. Powered by MaxMind GeoLite2-ASN, with hosting detection included.
ASN Meaning: What Does ASN Stand For?
ASN stands for Autonomous System Number — a globally unique identifier for a network on the internet. Every ASN is issued by a Regional Internet Registry and used in BGP routing to say which organization controls which IP addresses.
| Acronym | Stands for | What it means in practice |
|---|---|---|
ASN |
Autonomous System Number | The number itself, e.g. AS15169 for Google. |
AS |
Autonomous System | The network the number refers to. "AS lookup" and "ASN lookup" mean the same thing. |
BGP |
Border Gateway Protocol | How autonomous systems announce their IP prefixes to each other. |
RIR |
Regional Internet Registry | The body that assigns ASNs — ARIN, RIPE NCC, APNIC, LACNIC, or AFRINIC. |
CIDR |
Classless Inter-Domain Routing | The prefix notation an AS announces, e.g. 8.8.8.0/24. |
What Is an ASN Network?
An autonomous system is a set of IP prefixes operated under a single, coherent routing policy — usually by one ISP, hosting provider, cloud platform, or large enterprise. When people say "ASN network," they normally mean the block of IP addresses that a given ASN announces to the rest of the internet via BGP. Looking up an IP's ASN therefore tells you which network operator is responsible for that address, which is why it is such a useful signal for classifying traffic. Pair it with our IP geolocation API when you need the physical location alongside the network owner.
ASN in Networking vs. ASN in Nursing
"ASN" is an overloaded acronym. In healthcare it means Associate of Science in Nursing, and in logistics it means Advance Shipping Notice. This page covers ASN exclusively in the computer-networking sense: Autonomous System Numbers, BGP routing, and IP address ownership.
What Is an Autonomous System Number?
An Autonomous System Number (ASN) is a globally unique identifier assigned to a group of IP prefixes managed by one or more network operators under a single, clearly defined routing policy. The internet is not one network — it is tens of thousands of autonomous systems exchanging routing information with each other using the Border Gateway Protocol (BGP).
When your browser sends a request to a server, BGP tables built from ASN announcements determine the path your packets take across the internet. Each ASN announces the IP prefixes it "owns" to neighboring networks, and routers worldwide use this information to forward traffic to the right destination.
ASNs are assigned by the five Regional Internet Registries (RIRs): ARIN (North America), RIPE NCC (Europe/Middle East/Central Asia), APNIC (Asia-Pacific), LACNIC (Latin America), and AFRINIC (Africa). An organization typically applies for an ASN when it operates a network that exchanges routing information with two or more upstream providers (multi-homing), or when it provides transit to other networks.
BGP Routing
ASNs use BGP to announce IP prefixes they own to neighboring networks, building the global internet routing table.
5 Regional Registries
ARIN, RIPE NCC, APNIC, LACNIC, and AFRINIC assign ASNs to organizations in their respective geographic regions.
Fraud Detection
Datacenter ASNs (AWS, DigitalOcean) often indicate VPN or proxy usage. Residential ASNs signal genuine end-user traffic.
IP Prefixes
Each ASN announces one or more IP prefixes (CIDR blocks) it controls, from small /24 blocks to massive /8 allocations.
How to Do an ASN Lookup
Three ways to resolve an IP address to its autonomous system — the tool on this page, the JSON API, or the command line.
Paste an IP address into the lookup tool
Enter any IPv4 or IPv6 address in the lookup box above and press Look Up ASN. No account and no API key are required.
Read the ASN, organization, and prefix
You get four things back: the ASN itself (e.g. AS15169), the organization that
operates it, the network prefix in CIDR notation that covers the address you queried, and a
datacenter flag telling you whether the range belongs to hosting infrastructure rather than
a residential ISP.
Or call the API for the same data
One GET request returns the same fields as JSON, which is what you want if you are enriching logs or scoring signups in real time.
curl "https://ip-api.io/api/v1/asn/8.8.8.8?api_key=YOUR_API_KEY"ASN Lookup by IP Address
An ASN lookup always starts from an IP address: the registries publish which prefixes each autonomous system announces, so resolving an address to its AS is a matter of finding the most specific prefix that contains it. Both IPv4 and IPv6 work, and the answer is the operator of the network that address currently routes through — which for a VPN or cloud host is the provider, not the end user.
Find the IP Ranges Announced by an ASN
Worth being clear about the direction of the query: this tool and the
/api/v1/asn/{ip} endpoint go from an IP to its ASN and return the single
prefix covering that address. They do not enumerate every prefix an ASN announces. For a
complete prefix list, query your Regional Internet Registry's WHOIS service or a BGP
looking glass — those are the authoritative sources for full AS-to-prefix mappings.
ASN Lookup Tools and Checkers
If you prefer the command line, Team Cymru's WHOIS interface is the quickest ASN checker
available: whois -h whois.cymru.com " -v 8.8.8.8" returns the ASN, prefix, and
country in one line. dig works for reverse DNS, and each RIR runs its own
WHOIS server for registration detail. For looking up many addresses at once, see our
bulk IP lookup tool, which returns ISP and ASN for up to 100
addresses per request. If you want the geographic side of an address as well, the
IP geolocation API returns country, city, and timezone
alongside the network owner.
Major ASN List — Well-Known Autonomous System Numbers
Well-known Autonomous Systems operated by the world's largest internet organizations. Recognizing these ASNs helps classify traffic and build smarter fraud rules.
| ASN | Organization | Type | Region |
|---|---|---|---|
| AS15169 | Google LLC | Cloud / CDN | Global |
| AS13335 | Cloudflare, Inc. | CDN / DNS | Global |
| AS16509 | Amazon Web Services | Cloud | Global |
| AS8075 | Microsoft Corporation | Cloud / CDN | Global |
| AS32934 | Meta Platforms, Inc. | Cloud / Social | Global |
| AS20940 | Akamai Technologies | CDN | Global |
| AS14061 | DigitalOcean, LLC | Hosting / VPS | Global |
| AS63949 | Akamai Connected Cloud (Linode) | Hosting / VPS | Global |
| AS7922 | Comcast Cable Communications | ISP / Residential | North America |
| AS3215 | Orange S.A. | ISP / Residential | Europe |
| AS4134 | China Telecom | ISP / Residential | Asia-Pacific |
| AS174 | Cogent Communications | Tier-1 Transit | Global |
| AS3356 | Lumen Technologies (CenturyLink) | Tier-1 Transit | Global |
| AS9009 | M247 Europe SRL | VPN / Hosting | Europe |
| AS2914 | NTT Communications | Tier-1 Transit | Global |
| AS6939 | Hurricane Electric | Transit / IPv6 | Global |
| AS16276 | OVH SAS | Hosting / VPS | Europe |
| AS24940 | Hetzner Online GmbH | Hosting / VPS | Europe |
| AS45102 | Alibaba Cloud (US) LLC | Cloud | Asia-Pacific |
| AS9299 | Philippine Long Distance Telephone (PLDT) | ISP / Residential | Asia-Pacific |
ASN API — Look Up ASN by IP in One Request
A single GET request returns ASN, organization, network prefix, and datacenter classification. Predictable JSON — no parsing quirks.
GET /api/v1/asn/{ip}?api_key={key}
curl "https://ip-api.io/api/v1/asn/8.8.8.8?api_key=YOUR_API_KEY"
{
"ip": "8.8.8.8",
"asn": 15169,
"organization": "GOOGLE",
"network": "8.8.8.0/24",
"is_datacenter": true,
"country": "United States",
"country_code": "US"
}
GET /api/v1/asn/{ip}?api_key={key}
const res = await fetch(
"https://ip-api.io/api/v1/asn/8.8.8.8?api_key=YOUR_API_KEY"
);
const data = await res.json();
console.log(`AS${data.asn} — ${data.organization}`); // AS15169 — GOOGLE
console.log(data.is_datacenter); // true
{
"ip": "8.8.8.8",
"asn": 15169,
"organization": "GOOGLE",
"network": "8.8.8.0/24",
"is_datacenter": true,
"country": "United States",
"country_code": "US"
}
GET /api/v1/asn/{ip}?api_key={key}
import requests
res = requests.get(
"https://ip-api.io/api/v1/asn/8.8.8.8",
params={"api_key": "YOUR_API_KEY"}
)
data = res.json()
print(f"AS{data['asn']} — {data['organization']}") # AS15169 — GOOGLE
print(data['is_datacenter']) # True
{
"ip": "8.8.8.8",
"asn": 15169,
"organization": "GOOGLE",
"network": "8.8.8.0/24",
"is_datacenter": true,
"country": "United States",
"country_code": "US"
}
GET /api/v1/asn/{ip}?api_key={key}
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,
"https://ip-api.io/api/v1/asn/8.8.8.8?api_key=YOUR_API_KEY");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$data = json_decode(curl_exec($ch));
echo "AS{$data->asn} — {$data->organization}"; // AS15169 — GOOGLE
{
"ip": "8.8.8.8",
"asn": 15169,
"organization": "GOOGLE",
"network": "8.8.8.0/24",
"is_datacenter": true,
"country": "United States",
"country_code": "US"
}
GET /api/v1/asn/{ip}?api_key={key}
require 'net/http'
require 'json'
uri = URI('https://ip-api.io/api/v1/asn/8.8.8.8')
uri.query = URI.encode_www_form(api_key: 'YOUR_API_KEY')
res = Net::HTTP.start(uri.hostname, use_ssl: true) { |h| h.get(uri) }
data = JSON.parse(res.body)
puts "AS#{data['asn']} — #{data['organization']}" # AS15169 — GOOGLE
{
"ip": "8.8.8.8",
"asn": 15169,
"organization": "GOOGLE",
"network": "8.8.8.0/24",
"is_datacenter": true,
"country": "United States",
"country_code": "US"
}
ASN Lookup FAQs
Common questions about Autonomous System Numbers and BGP routing.
What is an ASN (Autonomous System Number)?
An Autonomous System Number (ASN) is a globally unique number assigned to a group of IP prefixes managed by one or more network operators under a single, coherent routing policy. ASNs are used in BGP (Border Gateway Protocol) to identify networks on the internet. Examples: AS15169 (Google), AS13335 (Cloudflare), AS16509 (Amazon Web Services).
What does ASN stand for?
ASN stands for Autonomous System Number. "AS" on its own stands for
Autonomous System — the network itself — while the ASN is the number assigned
to it, written with an AS prefix as in AS13335.
What is an ASN network?
"ASN network" normally refers to the set of IP prefixes that a given autonomous system announces to the internet through BGP. An autonomous system is a group of IP ranges operated under one routing policy, so its "network" is the collection of addresses it is responsible for routing — often millions of addresses for a large ISP or cloud provider.
Is an AS number lookup the same as an ASN lookup?
Yes. "AS lookup," "AS number lookup," "ASN lookup," and "IP to ASN" all describe the same operation: resolving an IP address to the autonomous system that announces it. The tool on this page handles all of them.
Does ASN mean anything other than Autonomous System Number?
It does — ASN is an overloaded acronym. In healthcare it means Associate of Science in Nursing, and in supply-chain systems it means Advance Shipping Notice. This page and this tool deal only with ASN in the computer-networking sense: Autonomous System Numbers used in BGP routing to identify who controls a block of IP addresses.
How do I find the ASN for an IP address?
Enter any IPv4 or IPv6 address into the lookup tool above and click "Look Up ASN." The tool
returns the ASN number, organization name, network prefix (CIDR), and whether the IP belongs to a
datacenter. For programmatic access, use GET https://ip-api.io/api/v1/asn/{ip}
with your API key.
What's the difference between an ASN and an IP address?
An IP address identifies a single device (or NAT boundary) on the internet. An ASN identifies an entire network or group of networks operated by one organization. One ASN can encompass millions of IP addresses. IP addresses tell you where traffic goes; the ASN tells you who controls the network that routes that traffic.
Who assigns ASNs?
ASNs are assigned by five Regional Internet Registries (RIRs) under the coordination of IANA: ARIN (North America), RIPE NCC (Europe, Middle East, Central Asia), APNIC (Asia-Pacific), LACNIC (Latin America & Caribbean), and AFRINIC (Africa). Organizations apply to their regional RIR when they need to exchange routing information with multiple upstream providers.
Can a company have multiple ASNs?
Yes. Large organizations often operate multiple ASNs for different regions, subsidiaries, or service categories. Amazon uses AS16509 for AWS, but also maintains several other ASNs for different parts of its infrastructure. Google, Meta, and Microsoft each operate dozens of ASNs globally. Each ASN represents a distinct autonomous system with its own routing policy.
How is ASN data useful for fraud detection?
ASN data reveals who controls the network an IP belongs to, which is a powerful fraud signal. Datacenter and hosting ASNs (DigitalOcean, AWS, Vultr) are frequently used by fraudsters to mask their location via VPNs or proxies. Legitimate users typically connect from residential ISP ASNs. Combine ASN classification with our Fraud Detection API for complete risk scoring.
What is BGP?
BGP (Border Gateway Protocol) is the routing protocol that connects autonomous systems on the internet. Each ASN uses BGP to announce the IP prefixes it controls to neighboring networks. Routers worldwide maintain BGP tables built from these announcements, enabling them to forward packets to the correct destination across thousands of interconnected networks. BGP is often called "the protocol that holds the internet together."
Is your ASN lookup tool free?
Yes, the interactive ASN lookup tool on this page is completely free with no sign-up required.
Programmatic API access (GET /api/v1/asn/{ip}) requires a paid subscription.
Anonymous users can make limited requests via the tool directly from this page.
Simple, transparent pricing
Start small, scale as you grow. No hidden fees.
Know who's behind any IP address
Query ASN number, organization, network prefix, and routing data in one simple API call.