1. Enter an IP or hostname
Use a public IPv4 or IPv6 address, or a hostname such as cloudflare.com. A hostname is resolved before the ASN query runs.
IP Protocol Tools
ASN Lookup for IP Addresses and Hostnames
Find the autonomous system and route prefix behind a public IP address, then use the result to understand the network carrying that traffic.
Origin ASNIdentify the autonomous system that originates the public route.
Prefix detailsSee routed prefix, registry, country, and allocation information.
Live lookupResolve hostnames and query current public ASN records.
Working tool
ASN Lookup
Enter a public IP address or hostname to find the originating autonomous system, route prefix, registry, country, allocation date, and network name.
Ready. Example input: 8.8.8.8
What does an ASN lookup show?
An ASN lookup connects a public IP address to the autonomous system that originates its route on the Internet. The result can include the ASN, network name, announced prefix, registry, country code, and allocation date. It helps identify the routing network behind an address, but it does not show the complete BGP path or prove who operates the website content.
How to use the ASN lookup
2. Check the prefix and ASN
The route prefix shows the address block being announced. The ASN identifies the routing domain originating that prefix.
3. Compare the result
Check whether the ASN matches the ISP, cloud provider, CDN, or security service you expected. Confirm important routing questions with a BGP looking glass.
What is an autonomous system number?
An autonomous system is a group of IP networks managed under a common routing policy. Its ASN is used in BGP route exchange between ISPs, cloud providers, CDNs, large enterprises, universities, and other networks.
Origin ASN
This is the autonomous system advertising the selected prefix to the public routing system. It may be a transit provider or CDN rather than the website owner.
Route prefix
The prefix is the network block associated with the returned origin. A more-specific route may have a different origin than a larger allocation containing it.
Registry and country
These fields describe registration context. They do not guarantee the physical location of the server or the path taken by every user.
ASN lookup examples
| Input | Typical output | Meaning |
|---|---|---|
| 8.8.8.8 | AS15169, GOOGLE, prefix 8.8.8.0/24 | The address is originated by Google's autonomous system. |
| cloudflare.com | Resolved IP plus AS13335 when DNS returns a Cloudflare edge address | Hostname results depend on DNS answer and CDN routing. |
Why an ASN result may be missing or unexpected
Private address
RFC1918, loopback, multicast, link-local, and documentation addresses are blocked because they do not have public BGP origin data.
No ASN found
The prefix may not be globally routed, the DNS data source may not have a record, or the address may be newly delegated.
Unexpected ASN
CDNs, Anycast, DNS load balancing, and cloud front doors can return an ASN different from the company that owns the domain.
When ASN information is useful
- Identify the ISP, cloud platform, CDN, hosting provider, or enterprise network behind a public address.
- Check whether a VPN, SD-WAN, or Internet circuit is exiting through the expected provider.
- Add routing context to firewall, proxy, WAF, mail, and SIEM investigations.
- Review the announced prefix before creating a narrowly scoped allowlist or block rule.
- Compare the origin with BGP monitoring data when troubleshooting a route leak or unexpected path.
ASN Lookup: FAQ
Is ASN the same as ISP?
Not always. An ASN identifies a routing domain. It may belong to an ISP, enterprise, cloud provider, university, exchange, or content network.
Can one ASN announce many prefixes?
Yes. Large networks often originate hundreds or thousands of IPv4 and IPv6 prefixes.
Does this show live BGP paths?
No. It identifies origin data for the address. Use BGP looking glass tools when you need path-by-path routing visibility.