An Autonomous System (AS) is a collection of IP networks and routers under the control of a single organization that presents a common routing policy to the internet. Each AS is identified by a unique Autonomous System Number (ASN).
Examples of organizations with their own AS include ISPs (like Deutsche Telekom – AS3320), large tech companies (Google – AS15169, Cloudflare – AS13335) and universities.
Autonomous Systems communicate with each other using BGP (Border Gateway Protocol) – the routing protocol of the internet. BGP allows ASes to announce which IP prefixes they can reach, enabling routers worldwide to find the best path for each packet.
| ASN | Organization | Type |
|---|---|---|
| AS3320 | Deutsche Telekom | ISP / Transit |
| AS15169 | Tech / Transit | |
| AS13335 | Cloudflare | CDN / Transit |
| AS16509 | Amazon AWS | Cloud / Transit |
| AS8075 | Microsoft | Tech / Transit |
The internet is not a single network but a collection of thousands of autonomous systems connected by BGP. Each AS is assigned a unique ASN by a regional internet registry (RIR). ISPs, cloud providers, universities and large companies all operate their own autonomous systems. Understanding ASNs helps explain how internet traffic is routed and why certain IP addresses belong to certain organizations.