Guide
What is an ASN?
An Autonomous System Number identifies the network that owns an IP address — the ISP, CDN or cloud behind it. How ASNs work, real examples, and how to read yours.
On this page
ASN in one paragraph
An Autonomous System Number is a globally unique ID (written AS + digits, e.g. AS13335) assigned to a network that runs its own routing policy — in practice, an ISP, a CDN, a cloud provider, a university or a large enterprise. Autonomous systems are the units the internet is wired together with: each one announces which address blocks it serves to the rest of the network via BGP, and every IP address belongs to exactly one ASN.
ASNs you will actually meet
| ASN | Organisation | What it means when it appears |
|---|---|---|
| AS13335 | Cloudflare | The site is behind Cloudflare — you are talking to an edge, not the origin |
| AS15169 | Google infrastructure (DNS, hosting, or a GCP customer range) | |
| AS16509 | Amazon (AWS) | Something running on Amazon Web Services |
| AS8075 | Microsoft | Microsoft / Azure network |
| AS3209 | Verizon (US) | A residential/business connection in the US |
The pattern: a small consumer address carries a national ISP's ASN; a streaming site carries a CDN's; a self-hosted blog carries its host's. One glance at the ASN separates "residential user" from "server in a rack" — that single distinction powers datacentre detection on this site and in most fraud engines.
How to find the ASN for any address
- This site: the home page and the lookup tool both show the ISP / organisation and ASN for any address, resolved from public registration data.
- Command line:
whois 1.1.1.1 | grep -iE 'origin|org-name|asn'shows the owning ASN and organisation. - RDAP: the modern REST replacement for WHOIS —
https://rdap.org/ip/1.1.1.1returns JSON with the registered organisation and the origin ASN. Tools and search engines mostly use this now.
Why it matters to you
- Reading a result: when a check shows "Organisation: Hetzner Online GmbH, AS24940", you are looking at a datacenter IP, whoever is behind it — the basis of the datacenter verdict.
- Trust: an ASN tells you who is legally responsible for the network — every registration lists an abuse contact for reporting.
- Network identity: large operators run several ASNs; a company you know as one brand may show up under different numbers on different connections.
Related: what an address reveals in general (what is an IP address) and how ownership is registered (WHOIS and RDAP).
Frequently asked questions
Is the ASN the same as my ISP?
Usually the ASN you see is owned by your ISP, but large providers operate many ASNs, and some small ISPs borrow their upstream's. The ASN names the network, the ISP name names the customer-facing brand.
Can one company own multiple ASNs?
Yes — common for cloud and CDN companies, which consolidate or split ranges for operational reasons. The number changes, the company behind it often does not.
Does an ASN reveal who is browsing?
No. It identifies the network an address belongs to — an ISP or a host — not the person or household using it.
Keep reading
- What is an IP address?
- Public vs private IP addresses
- IPv4 vs IPv6
- How to hide your IP address
- How to check your IP address on a phone
- What is CGNAT?
- How to change your IP address
- Why does my IP address keep changing?
- How to find a website's IP address
- What is a datacenter IP?
- IPv6 privacy extensions
- How IP geolocation works
- What is a local IP address?
- Why am I getting blocked or stuck on CAPTCHAs?
- What is IP reputation?
- How websites detect VPNs and proxies
- What is a DNS leak?
- What is a WebRTC leak?
- Proxy vs VPN
- How to check if your VPN actually works
- Static vs dynamic public IP
- How to find out who owns an IP address
- IPv6 in 2026
- Check my public IP address
Check any other IP address
Investigating a suspicious login, a spam email header or a server log entry? Run any IPv4 or IPv6 address through the same geolocation and proxy checks.