What is an ASN, and what does it identify?¶

An Autonomous System Number identifies a network that presents a common routing policy to the wider internet.

The short version¶

An ASN helps identify a network involved in announcing or carrying an address range. It does not normally identify the subscriber, device or person using one address.

Internet providers, cloud companies, universities and content-delivery networks may operate ASNs. A network can announce routes for its own range, another organisation’s range or customers reached through a reseller or upstream provider.

Interpret it in time¶

Routing arrangements change. A current ASN result may not describe the path or provider relationship at the event time. The organisation registered for an address range may also differ from the organisation announcing it.

Use the ASN to classify infrastructure and identify a possible record holder. Then check historical routing, registration, allocation and customer records.