What Is an ASN?
An ASN (Autonomous System Number) identifies a network or group of networks on the public internet. ISPs, cloud providers, CDNs, hosting companies, universities, and large organizations use ASNs so their networks can exchange routing information with other networks using BGP (Border Gateway Protocol).
When you look up an IP address and see an ASN in the results, it tells you which network operator announces or manages the IP range. This is useful for identifying hosting providers, investigating traffic sources, and understanding network infrastructure.
How ASNs work with BGP
BGP is the routing protocol networks use to tell each other which IP address ranges they can reach. Each network identifies itself with its ASN when exchanging routes. The AS path — the sequence of ASNs a route passes through — helps routers make forwarding decisions and helps analysts trace routing behavior.
What ASN lookups show
- The autonomous system number (e.g., AS13335 for Cloudflare)
- The organization or network name associated with the ASN
- The Regional Internet Registry (RIR) that manages the record
- Related IP prefixes announced by the network
- Routing and peering context
Common uses
- Security triage: Group suspicious IPs by ASN to see if they share a common hosting provider or network.
- Hosting verification: Confirm whether a service is hosted on the expected cloud provider or CDN.
- Network research: Understand the scale and structure of an organization's internet presence.
- Abuse reporting: Identify the correct network operator to contact about abusive traffic.
Limitations
An ASN identifies a network operator, not an individual user. Many different customers and services may share the same ASN. ASN data provides infrastructure context, not personal identity information.