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What is an ASN?
Autonomous System Numbers identify the networks that route traffic across the internet.
An autonomous system is a large network, or group of networks, that presents a unified routing policy to the rest of the internet. Internet service providers, cloud platforms, universities, and large companies often operate one.
An Autonomous System Number, usually shortened to ASN, is the unique identifier assigned to that network. Routers use ASNs in BGP announcements to decide where traffic should go next.
When an IP address maps to an ASN, it usually tells you which provider or organization is announcing that address range. That can help explain why an address appears to belong to a cloud host, mobile carrier, enterprise network, or VPN provider.
The ASN alone does not prove who is using a specific IP address at a given moment. It only points to the network that currently originates the route.