Glossary
What is an ASN?
An Autonomous System Number (ASN) is a globally unique identifier assigned to a network — typically an ISP, cloud provider, CDN, or large organization — that announces IP address prefixes on the Internet via BGP (Border Gateway Protocol).
ASNs are 16-bit or 32-bit integers. Examples of well-known ASNs:
When you visit a website, your packets typically traverse 3–7 ASNs on their way: your home ISP → possibly a transit provider → a CDN or cloud AS → the destination AS. Each ASN runs its own router fleet and peering relationships.
There are about 77,000 active ASNs globally. WorldIP.io tracks every one: browse all ASNs.
