Find the autonomous system number behind any IP address.
Enter an IP address to see the AS number and network it belongs to. It is free, with no signup.
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An ASN lookup finds the autonomous system number that an IP address belongs to. An autonomous system, or AS, is a network run under one routing policy, and its number identifies it on the internet. 1Lookup's free ASN lookup takes an IPv4 or IPv6 address and returns its AS number, network name, ISP, organization and country.
- Free, no signup
- IPv4 and IPv6
- AS number and network name
- Works from an IP address
You can find an IP address's ASN in under a minute.
Enter the IP address.
Type an IPv4 or IPv6 address, such as 8.8.8.8.
Read the AS number.
The result shows the number, such as AS15169, and the network name the registry gives it.
Read the network behind it.
The ISP, the organization and the country sit beside the number.
Go to the registry for the AS record.
To read a registry's own record for an AS number, ask the regional registry that issued it: ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC.
Need this at scale? IP Lookup API
The ASN, ISP and organization behind every IP address, with VPN, proxy and fraud flags, in real time.
An ASN lookup names the network an IP address belongs to, and that network is an autonomous system.
The internet is a network of networks, and each network that sets its own routing policy is an autonomous system, or AS. RFC 1930 defines an AS as a connected group of one or more IP prefixes run by one or more network operators that has a single and clearly defined routing policy. Each AS has a number, its ASN, and an IP address belongs to the AS that announces the range it sits in.
A lookup answers a simple question: which network is this address on? That is the first thing to know about traffic you do not recognize. An address in a home internet provider's AS is typically a household or office connection, while one in a hosting company's AS is typically a server.
AS numbers are handed out by the five regional internet registries, and the Number Resource Organization publishes their combined statistics. In its file of 23 October 2026, 122,984 AS numbers are assigned, 32,285 of them to the United States.
This tool works from an IP address. It does not take an AS number as input, so to go from an AS number to the registry's record for it, ask the registry that issued it.
The IP lookup API returns the ASN with location and fraud signals for every address.
When the check has to run inside your own software or across a log file, the API returns the AS number, ISP, organization, location and VPN, proxy and datacenter flags for each address for 1 credit a lookup. See the IP lookup API. To see an address's city, region and connection type, use our free IP address lookup. To get a fraud score for an address, use our free IP fraud score checker. To see whether an address is a VPN or a proxy, use our free VPN and proxy detection. To see whether an address is on a blocklist, use our free IP blacklist check.
An ASN lookup returns these fields, and each one answers a different question.
This is an invented result for 203.0.113.42, an address set aside for examples, laid out the way a lookup comes back. The first five fields are free on this page, and a free account opens the rest.
- AS numberAS64496
- Network nameExample Networks
- ISPExample Networks
- OrganizationExample Networks Inc
- CountryUnited States
Opens with a free trial
- Fraud risk score25 out of 100
- VPN / proxy detectionMedium
- Connection typeDatacenter
- Risk factors behind the scoreDATACENTER_IP
AS number
The autonomous system number of the network the address belongs to. AS64496 is one of the numbers set aside for documentation, so it stands in for a real one.
Network name
The name the network goes by in the record.
ISP
The internet service provider for the address, as the record names it.
Organization
The organization the address block is registered to.
Country
The country the address is located in. It comes from the address's location, and the AS number itself carries no country.
Fraud risk score
The 0 to 100 score for the address, with its risk level.
VPN / proxy detection
How likely the address is a VPN or proxy exit, shown as low, medium or high.
Connection type
The kind of connection the address uses, such as datacenter, mobile or proxy, read from the address's network flags.
Risk factors behind the score
The reasons the score lists, such as a datacenter address or a missing reverse DNS name.
The lookup finds the AS number from the IP address in three steps.
You enter an IP address.
Type or paste an IPv4 or IPv6 address. A private or reserved address is told apart, because no AS announces it.
We read the address's network record.
1Lookup reads the AS number and name, the ISP and the organization the address belongs to.
You read the AS number and the network.
See the number, the name, the ISP, the organization and the country. A free account opens the fraud score and VPN checks for the same address.
An ASN lookup reads the address's network record, then names the AS and its network.
This is the path one lookup takes. The AS number and the network name come from the address's own record.
- You enter the addressAn IPv4 or IPv6 address.
- Its network record is readThe AS the address sits in, with the ISP and the organization.
- The number and name are splitAS15169 and its network name come back as two fields.
- You read the resultThe AS number, name, ISP, organization and country. A private address says it has no AS.
RIPE NCC and ARIN together hold 60.4% of the 122,984 AS numbers assigned.
The five regional internet registries hand out AS numbers, each for its own part of the world. This is how many each had assigned in the Number Resource Organization's file of 23 October 2026.
| Registry | Region it serves | AS numbers assigned | Share |
|---|---|---|---|
| RIPE NCC | Europe, the Middle East and parts of Central Asia | 40,072 | 32.6% |
| ARIN | The United States, Canada and many Caribbean and North Atlantic islands | 34,249 | 27.8% |
| APNIC | Asia Pacific | 31,432 | 25.6% |
| LACNIC | Latin America and the Caribbean | 14,415 | 11.7% |
| AFRINIC | Africa | 2,816 | 2.3% |
Source: NRO extended delegated statistics, file of 23 October 2026.
Between 4,758 and 5,263 new AS numbers have been assigned each year since 2022, after a one-off 11,226 in 2021.
The Number Resource Organization's file gives the date each AS number was assigned. This table counts them by year for the 10 full years from 2016 to 2025. The file's current year is left out because it is not over.
| Year assigned | AS numbers assigned |
|---|---|
| 2016 | 4,806 |
| 2017 | 5,132 |
| 2018 | 5,631 |
| 2019 | 5,896 |
| 2020 | 6,313 |
| 2021 | 11,226 |
| 2022 | 4,758 |
| 2023 | 4,958 |
| 2024 | 5,184 |
| 2025 | 5,263 |
Source: NRO extended delegated statistics, file of 23 October 2026.
The United States holds 32,285 AS numbers, 26.3% of the total, and no other country holds more than 9,179.
The ten countries with the most AS numbers in the Number Resource Organization's file of 23 October 2026, which lists 242 country codes in all. The country is the one the registry records for the holder, not where traffic flows.
| Country | Code | AS numbers assigned | Share |
|---|---|---|---|
| United States | US | 32,285 | 26.3% |
| Brazil | BR | 9,179 | 7.5% |
| China | CN | 6,627 | 5.4% |
| India | IN | 6,308 | 5.1% |
| Russia | RU | 5,774 | 4.7% |
| Indonesia | ID | 4,075 | 3.3% |
| Germany | DE | 3,257 | 2.6% |
| United Kingdom | GB | 3,136 | 2.5% |
| Australia | AU | 3,004 | 2.4% |
| Canada | CA | 2,521 | 2.0% |
Source: NRO extended delegated statistics, file of 23 October 2026.
Eight blocks of AS numbers are set aside for private use, documentation or reserved purposes.
IANA keeps the list of AS numbers that no registry hands to a single public network. An address can still show one of them, which is why the lookup tells a private or reserved record apart from a real one.
| AS numbers | Set aside for | Reference |
|---|---|---|
| 0 | Reserved | RFC 7607 |
| 23456 | AS_TRANS, a stand-in for 4-byte AS numbers | RFC 6793 |
| 64496 to 64511 | Documentation and sample code | RFC 5398 |
| 64512 to 65534 | Private use | RFC 6996 |
| 65535 | Reserved | RFC 7300 |
| 65536 to 65551 | Documentation and sample code | RFC 5398 |
| 4200000000 to 4294967294 | Private use | RFC 6996 |
| 4294967295 | Reserved | RFC 7300 |
Nine well-known networks were assigned their AS numbers between 1993 and 2010.
Registry, country and date are from the Number Resource Organization's file of 23 October 2026, and the network names are the ones the registries show in their own records. The date is when the number was assigned, so a number can be older than the network's fame.
| AS number | Name in the registry | Registry | Country | Assigned |
|---|---|---|---|---|
| AS1299 | TWELVE99 | RIPE NCC | SE | September 1, 1993 |
| AS174 | COGENT-174 | ARIN | US | May 16, 1996 |
| AS8075 | MICROSOFT-CORP-MSN-AS-BLOCK | ARIN | US | March 31, 1997 |
| AS9498 | BBIL-AP | APNIC | IN | March 9, 1999 |
| AS15169 | ARIN | US | March 30, 2000 | |
| AS16509 | AMAZON-02 | ARIN | US | May 4, 2000 |
| AS4134 | CHINANET-BACKBONE | APNIC | CN | August 1, 2002 |
| AS32934 | ARIN | US | August 24, 2004 | |
| AS13335 | CLOUDFLARENET | ARIN | US | July 14, 2010 |
Source: NRO extended delegated statistics, file of 23 October 2026.
RFC 1930 says a site with one connection needs no AS number, so its address shows its provider's.
RFC 1930, published in March 1996, sets out when a network should create its own AS. It is why a small customer's address shows the ISP's AS number and not its own.
| Situation | Needs its own AS? | What RFC 1930 says |
|---|---|---|
| A site with one connection and one prefix | No | A separate AS is not needed, and the prefix should be placed in an AS of the provider. |
| A site with one connection and several prefixes | No | A separate AS is not needed, and the prefixes should be placed in an AS of the site's provider. |
| A site connected to more than one service provider | Yes | An AS is required, and this is almost the only case where a network operator should create its own AS number. |
| A site that needs a routing policy different from its provider's | Yes, rarely | A separate AS must be created for the affected prefixes, but this should almost never happen. |
Source: RFC 1930, Guidelines for creation, selection, and registration of an Autonomous System.
An ASN lookup costs 1 credit, about $4.95 per 1,000 lookups on Starter and $2.00 on Enterprise.
These are the monthly plans on the pricing page. The AS number, ISP and organization come back on the same lookup as the location, every plan starts with a 7-day free trial, and the same credits pay for every other 1Lookup check.
| Plan | About per 1,000 lookups | Monthly price | ASN lookups included |
|---|---|---|---|
| Starter | $4.95 | $99 | 20,000 |
| Growth | $3.52 | $299 | 85,000 |
| Professional | $3.20 | $799 | 250,000 |
| Enterprise | $2.00 | $1,999 | 1,000,000 |
You can look up the ASN of a whole list of IP addresses with one CSV file.
The free tool checks one address at a time. With a 1Lookup account you upload a CSV file, pick the column that holds the addresses and download the same file back with the network columns filled in on every row. These are 5 of the columns it adds, with invented addresses.
| ip | Country | ISP | ASN | Organization | Connection Type |
|---|---|---|---|---|---|
| 203.0.113.42 | United States | Example Networks | AS64496 Example Networks | Example Networks Inc | DATACENTER |
| 198.51.100.17 | United States | Sample Wireless | AS64497 Sample Wireless | Sample Wireless LLC | MOBILE_NETWORK |
| 192.0.2.88 | Canada | Demo Networks | AS64498 Demo Networks | Demo Networks Ltd | UNKNOWN |
- 1 credit an address, the same price as one API lookup.
- Up to 2 million rows in one CSV file.
- Up to 1,000 API requests a minute on every account.
The IP lookup API returns the ASN as JSON from one request.
Send the address to the IP endpoint with your API key. Each request costs 1 credit, and every account can send up to 1,000 requests a minute. The AS number and its name come back together as one string in insights.network.asn, such as AS64496 Example Networks, and the ISP and organization sit beside it in insights.network.
curl -X POST https://app.1lookup.io/api/v1/ip \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{"ip": "203.0.113.42"}'import requests
response = requests.post(
"https://app.1lookup.io/api/v1/ip",
headers={"Authorization": "Bearer YOUR_API_KEY"},
json={"ip": "203.0.113.42"},
)
data = response.json()["data"]
print(data["insights"]["network"]["asn"])const response = await fetch('https://app.1lookup.io/api/v1/ip', {
method: 'POST',
headers: {
'Authorization': 'Bearer YOUR_API_KEY',
'Content-Type': 'application/json'
},
body: JSON.stringify({ ip: '203.0.113.42' })
})
const { data } = await response.json()
console.log(data.insights.network.asn)Response
{
"success": true,
"data": {
"request": { "type": "ip", "input": "203.0.113.42" },
"insights": {
"network": {
"isp": "Example Networks",
"org": "Example Networks Inc",
"asn": "AS64496 Example Networks"
},
"location": { "country": "United States", "country_code": "US" }
},
"metadata": { "credits_used": 1, "credits_remaining": 9998 }
}
}To run the same lookup from your own software or on every signup, see our IP lookup API.
It splits the AS number from the network name.
The number and the name come back as separate fields, so the number can be copied on its own.
It tells a private address from a public one.
An address in private or reserved space has no AS number, and the result says so instead of showing an empty field.
It names the cloud when the address is in one.
An address that falls in a published cloud range shows the cloud provider and region beside the AS number.
It covers IPv4 and IPv6.
Both address families are read, so an address from a log file works whichever form it takes.
Who uses this tool
Security teams use it to see whose network an address is on.
An address in a log that no one recognizes becomes a network name and an AS number that can be searched or blocked as a group.
Fraud and trust teams use it to spot signups from hosting networks.
An address in a hosting company's AS is a different signal from one in a home provider's, and the fraud score for the same address is one step further.
Network engineers use it to confirm who owns an address in a trace.
The AS number and name answer which network an address belongs to without a manual registry search.
Support teams use it to see which provider a customer is on.
A customer's address shows the ISP and AS, which helps when a problem only affects one provider's customers.
Frequently asked questions
What is an ASN?
An ASN is an autonomous system number. RFC 1930 defines an autonomous system as a connected group of one or more IP prefixes run by one or more network operators with a single and clearly defined routing policy, and the ASN is the number that identifies it.
How do I find the ASN of an IP address?
Enter the address in this lookup. It returns the AS number, written as AS followed by digits, together with the network name, the ISP, the organization and the country.
What does an AS number look like?
It is written AS followed by a number, such as AS15169. The IANA registry lists AS numbers up to 4,294,967,295, with the highest blocks set aside for private use and reserved.
How many ASNs are there?
122,984 AS numbers are assigned in the Number Resource Organization's statistics file of 23 October 2026, spread across 242 country codes.
Who assigns AS numbers?
The five regional internet registries do: ARIN, RIPE NCC, APNIC, LACNIC and AFRINIC. Each serves a region of the world, and the Number Resource Organization publishes their statistics together.
Can I look up an ASN from an AS number?
Not with this tool, which takes an IP address. To read the registry's record for an AS number, ask the regional registry that issued it.
Does every IP address have an ASN?
A public address that is announced on the internet sits in an AS. Private and reserved addresses are not announced, so the result says that no AS number was found.
Why does my address show my provider's ASN and not my company's?
RFC 1930 says a site with a single connection does not need an AS of its own, and that its prefix should be placed in an AS of its provider. A small customer's address therefore shows the provider's AS.
What is a private ASN?
AS numbers 64512 to 65534 and 4200000000 to 4294967294 are set aside for private use (RFC 6996). They are not assigned to any one organization.
Why do the examples use AS64496?
AS numbers 64496 to 64511, and 65536 to 65551, are reserved for documentation and sample code (RFC 5398), so an example never points at a real network.
Is the ASN the same as the ISP?
No. An ISP is a company, and an ASN is a network identifier. One organization can hold more than one AS number, so the result shows the AS number, the network name and the ISP as separate fields.
Does the ASN tell me where a user is?
No. An AS number names a network, and a network can span countries. The country in the result is where the address is located, which is a separate lookup from the AS record.
How much does an ASN lookup cost per lookup in the API?
An ASN lookup costs 1 credit per address in the API or a CSV upload, the same as any IP lookup. That is about $4.95 per 1,000 on the Starter plan, $3.52 on Growth, $3.20 on Professional and $2.00 on Enterprise. The free tool on this page checks one address at a time with no signup, and every plan starts with a 7-day free trial.
Is there an API that returns the ASN for a list of IP addresses?
Yes. The 1Lookup IP lookup API returns the ASN with the ISP, organization, location and VPN, proxy and datacenter flags, one address at a time in real time or for whole lists from a CSV upload, starting with a 7-day free trial.
Is this ASN lookup really free?
Yes. The tool is free to use online and rate-limited for fair access, and it needs no signup. To see the fraud score and VPN checks for an address, or to look up addresses in bulk, sign up for a 7-day free trial, then use the API as you scale.
These pages answer the question that comes after an ASN lookup.
- IP address lookupThe city, region, ISP and connection type behind an address.
- IP fraud score checkerA fraud risk level for an address, with its VPN and datacenter signals.
- VPN and proxy detectionWhether an address is a VPN, a proxy or a Tor exit.
- IP blacklist checkWhether an address is on a public blocklist.