What is an ASN and Why Does It Appear on IP Lookups?

An Autonomous System Number (ASN) is a unique identifier assigned to a network that operates on the internet.

Examples you will often see:

• AS15169 — Google LLC
• AS13335 — Cloudflare, Inc.
• Your ISP’s ASN

Knowing the ASN tells you who owns and operates the network behind an IP address. It is extremely useful for network troubleshooting, abuse reporting, and understanding who controls a particular connection.