# Autonomous System Numbers

An Autonomous System (AS) is a group of one or more IP prefixes (lists of IP addresses accessible on a network) run by one or more network operators that maintain a single, clearly-defined routing policy. Network operators need Autonomous System Numbers (ASNs) to control routing within their networks and to exchange routing information with other Internet Service Providers (ISPs). Reference.

NetSPI manually identifies ASNs by searching for yours and your subsidiaries' legal names in our ASN data provider and associating them with your attack surface. IP addresses for all discovered ASNs are automatically added to your attack surface.