ASN Lookup
An Autonomous System Number (ASN) identifies a network under a single administrative domain - Such as an ISP, hosting provider, or large corporation. Enter an IP address to look up its ASN and routing organisation.
What Is an ASN?
An Autonomous System (AS) is a collection of IP address ranges managed by one or more network operators with a common routing policy. Every AS is identified by a unique ASN assigned by regional internet registries (RIRs) such as ARIN, RIPE, APNIC, LACNIC, and AFRINIC. For a full introduction to autonomous systems and BGP, read our guide on what an ASN is.
Common Uses
- Identifying the ISP or hosting provider behind an IP
- Network route analysis and BGP troubleshooting
- Security research and threat intelligence
- Detecting whether an IP belongs to a datacenter or residential network
How ASN Lookup Works
When you submit an IP address or domain, the tool first resolves it to an IP, then queries routing and registry data to find which Autonomous System currently announces that address. The result includes the AS number itself, the registered AS name and organisation, the country where the network is registered, and the regional internet registry (ARIN, RIPE, APNIC, LACNIC, or AFRINIC) that allocated it.
Where available, the lookup also returns the number of IPv4 and IPv6 prefixes the AS announces, which gives a sense of the network's size. A residential ISP typically announces hundreds of prefixes covering millions of addresses, while a small hosting company may announce only one or two. Because BGP announcements change over time, an IP can occasionally move between ASNs - For example when an address block is sold or a company changes upstream providers.
ASN data is one of the most reliable ways to attribute an IP address. Geolocation can be vague or wrong, but the announcing AS is taken directly from the live routing table, so it tells you with high confidence which organisation is operationally responsible for the address. Our explainer covers how Autonomous System Numbers work.
Common ASN Examples
Large internet companies operate some of the most recognisable Autonomous Systems. If a lookup returns one of these ASNs, the IP belongs to that company's network:
| ASN | Organisation | Typical use |
|---|---|---|
AS15169 | Google LLC | Google search, Gmail, Google Cloud, 8.8.8.8 DNS |
AS13335 | Cloudflare, Inc. | CDN, DDoS protection, 1.1.1.1 DNS |
AS32934 | Meta Platforms, Inc. | Facebook, Instagram, WhatsApp infrastructure |
AS16509 | Amazon.com, Inc. | Amazon Web Services (EC2, S3, CloudFront) |
AS8075 | Microsoft Corporation | Azure, Office 365, Outlook, Xbox Live |
Seeing a datacenter ASN like these behind a "residential" visitor is a strong hint that the connection is coming from a cloud server, VPN, or bot rather than a home user.
What an ASN Lookup Tells You That an IP Lookup Does Not
An IP lookup answers "where is this address, roughly". An ASN lookup answers "who operates the network it belongs to, and how big is that network". That second question is usually the more useful one.
- Hosting vs residential - An address inside a datacenter ASN behaves very differently from one inside a consumer ISP ASN. This is the primary signal behind most proxy and VPN detection.
- Scope of a problem - If several addresses causing trouble share one ASN, you are dealing with one network, not several unrelated sources.
- Who to contact - Abuse reports go to the operator of the announcing ASN, not to the geographic location the IP maps to.
- Routing reality - The announced prefix shows the actual block being routed, which is often far larger or smaller than a single address suggests.
How Addresses Get Assigned to an ASN
- IANA allocates large blocks of address space to the five Regional Internet Registries (ARIN, RIPE NCC, APNIC, LACNIC, AFRINIC).
- Each RIR assigns smaller blocks, and AS numbers, to networks in its region.
- The network announces its prefixes over BGP to its peers, declaring "traffic for this block should come to me".
- Those announcements propagate globally, and the resulting routing table is what an ASN lookup reads.
Because assignment and announcement are separate steps, a block can be assigned to one organisation but announced by another - which is exactly what you are seeing when a lookup returns an unexpected operator.
Frequently Asked Questions
What is an ASN used for?
An ASN identifies a network on the internet for BGP routing. Network operators use ASNs to exchange routing information, while analysts use them to attribute IP addresses to an ISP, hosting provider, or company, and to build security block or allow lists at the network level.
How do I find my ISP's ASN?
Enter your own public IP address into the lookup above - The result shows the ASN and organisation name of the network announcing it, which for home connections is almost always your ISP. You can find your public IP on the WhatsMyIP.now home page.
What is the difference between public and private ASNs?
Public ASNs (most numbers below 64512, plus the 32-bit public range) are globally unique and visible in the internet routing table. Private ASNs (64512-65534 and 4200000000-4294967294) are reserved for internal use, such as routing between a customer and their ISP, and are never announced to the global internet.
Related Tools
Sources & Further Reading
The technical claims on this page are drawn from the primary specifications and vendor documentation below.