DNS & Glossary

ASN (Autonomous System Number)

The number that identifies a network operator on the internet. Every IP address belongs to an AS, so the ASN reveals who hosts or routes a given address.

What it is

An Autonomous System is a collection of IP prefixes under one routing policy — an ISP, cloud provider or large enterprise. Its ASN (e.g. AS15169 for Google) is what BGP uses to exchange routes. Looking up an IP's ASN tells you which organisation operates the network hosting it.

Why it matters

  • It reveals the true hosting/network operator behind an IP, useful for security and provider detection.
  • It is the unit of internet routing via BGP.

Common mistakes

  • Assuming the ASN owner is the website owner — hosting and CDN providers own the AS, not the site.

How WebInspect checks this

  • The Network Inspector reports the ASN, AS organisation and BGP prefix for the target IP.