ZenovayTools

ASN Lookup

Look up the Autonomous System Number (ASN), organization, country, and IP prefix for any IP address or domain. Uses Cymru DNS-based IP-to-ASN service for real-time lookups.

How to Use ASN Lookup

  1. 1Enter an IP address or domain name.
  2. 2The tool resolves domains to IP and queries the Cymru ASN database via DNS.
  3. 3The ASN number, organization name, country, and network prefix are returned.
  4. 4Use this to identify who owns an IP range or investigate network routing.
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Frequently Asked Questions

What is an ASN (Autonomous System Number)?▾
An Autonomous System Number (ASN) is a unique identifier assigned to a network or group of IP addresses that are managed by a single organization and share a common routing policy. ASNs are used in BGP (Border Gateway Protocol), the routing protocol that powers the internet. Every IP address belongs to an ASN. Large ISPs, cloud providers (AWS AS16509, Google AS15169, Cloudflare AS13335), and enterprises each have their own ASN. ASNs are assigned by Regional Internet Registries (RIRs): ARIN (North America), RIPE NCC (Europe), APNIC (Asia-Pacific), LACNIC (Latin America), AFRINIC (Africa).
What can I use ASN lookups for?▾
Common uses: (1) Identify which cloud provider or ISP hosts a website or API server. (2) Security analysis — determine if traffic comes from a known cloud ASN (AWS, Azure) vs residential or suspicious ASNs. (3) Network troubleshooting — understand routing paths and providers. (4) Firewall rules — block or allow entire ASN ranges for geofencing or cloud provider access control. (5) Investigate spam or DDoS sources — identify the organization responsible for an attacking IP. (6) Competitor analysis — identify which CDN or hosting provider a website uses.
What is the difference between ASN, ISP, and hosting provider?▾
An ASN is the technical identifier for a network block. The organization field shows who owns and operates that ASN — this could be an ISP (Comcast, BT, Deutsche Telekom), a cloud hosting provider (Amazon, Google, Microsoft, Hetzner), a CDN (Cloudflare, Fastly, Akamai), a university, or a large enterprise. The prefix shows the specific IP range (CIDR block) that contains your IP. The registry shows which RIR manages the allocation. The country shows where the network is registered (not necessarily where the server is physically located).
Why does country differ from the server's actual location?▾
The country in ASN data reflects where the network block is registered with the Regional Internet Registry, not the physical location of the server. For example, AWS might have IP blocks registered in the US even if the actual EC2 server is running in a European datacenter. Cloudflare uses anycast routing, so the same IP might physically terminate in many countries. For precise geolocation, use dedicated IP geolocation databases (MaxMind GeoIP, ip-api.com) which use additional signals beyond ASN registration.
How does this tool look up ASN data?▾
This tool uses the Team Cymru IP-to-ASN DNS service — a free, DNS-based lookup that maps IP addresses to ASN data. For any IP like 8.8.8.8, the IP is reversed (8.8.8.8 → 8.8.8.8) and looked up at `8.8.8.8.origin.asn.cymru.com` as a TXT record. The response contains the ASN, IP prefix, country, registry, and allocation date. Then `AS15169.asn.cymru.com` is queried to get the organization name. All queries use DNS-over-HTTPS (Cloudflare 1.1.1.1) for privacy and reliability.