What is an ASN?
An Autonomous System Number (ASN) identifies a network — or group of networks — operated under a single routing policy on the internet, typically an ISP, hosting provider, or large organization. Every ASN announces one or more blocks of IP addresses (prefixes) to the rest of the internet via BGP, the protocol that routes traffic between networks.
Why look one up?
Common reasons include identifying who actually operates an IP address you've seen in logs, auditing which IP ranges belong to a known provider (e.g. for firewall or allow-list rules), or investigating the network path traffic takes to reach your server.
Lookups happen live and aren't stored. See our privacy page for details.