What is an ASN
When you use my IP Lookup tool, one of the fields it shows is an ASN — something like AS15169 (Google) or AS7922 (Comcast). ASN stands for Autonomous System Number, and understanding what it represents gives you a much clearer picture of how internet traffic travels from your device to anywhere in the world.
The internet is a network of networks
Most people think of the internet as a single global network. It is more accurate to think of it as thousands of separate networks interconnected. Every ISP, large company, university, and cloud provider that connects to the internet operates its own network — its own collection of routers, cables, and IP address ranges. These individual networks are called Autonomous Systems.
An Autonomous System is a network or group of networks that operates under a single administrative entity and uses a single, clearly defined routing policy. Your home ISP is an AS. Cloudflare is an AS. Google is several ASes. AWS is many ASes. Each controls its own IP address ranges and makes its own decisions about routing.
How ASNs work in practice
Each Autonomous System is assigned a unique number by one of the five regional internet registries: ARIN (North America), RIPE NCC (Europe), APNIC (Asia-Pacific), LACNIC (Latin America), and AFRINIC (Africa). This number identifies the AS in the global routing system called BGP (Border Gateway Protocol).
BGP is the routing protocol that lets different Autonomous Systems exchange information about which IP address ranges they are responsible for. When you send a request to a server on the other side of the world, it passes through multiple Autonomous Systems — each using BGP to decide the next hop toward the destination. BGP is called "the protocol that runs the internet" because without it, traffic would have no way to route across organisational boundaries.
Why ASNs are publicly visible
ASN information is publicly registered — that is the whole point. The routing tables that make the internet function rely on everyone being able to see which IP ranges belong to which AS. This is why IP lookup tools can show your ASN: the registration data mapping IP ranges to ASNs is publicly available in routing databases like the RIPE database and ARIN whois.
What your ASN reveals
Your ASN immediately identifies your ISP or network provider. AS15169 is Google. AS7922 is Comcast. AS13335 is Cloudflare. A data centre IP will belong to a hosting company's AS; a residential IP belongs to an ISP's AS. This distinction matters for anti-bot detection (data centre ASNs indicate VPNs or automation), streaming geo-restrictions, and network debugging. If you are having routing issues, looking at which AS your traffic is passing through can help identify where the problem originates.