Network operator and ASN

An autonomous system number, or ASN, helps identify the network that directs internet traffic for an IP address. It identifies an autonomous system: a set of networks and routers managed under shared rules for directing traffic. Looking up an IP address's ASN can help identify the network that tells other networks it can carry traffic to that address, often a provider or organization.

What can an ASN lookup tell you?

IP address ranges are associated with network operators, and routing systems use ASNs to distinguish those networks. For example, a lookup for a website's IP may show an ASN registered to a cloud provider. That suggests the address is routed through that provider's network; it does not necessarily identify the website owner, the physical server location, or the company responsible for the website's content.

One organization can use multiple ASNs, and a network may announce that it can carry traffic to an address on behalf of a customer. A website behind a CDN may show the CDN's network rather than the origin hosting provider. Registration data for ASNs and IP blocks is maintained through regional Internet registries and IANA allocation processes.

Related terms

• IP address — the network address being looked up
• Content delivery network — may announce routes for the addresses visitors reach
• Reverse DNS and PTR record — a separate name lookup
• Origin server — may sit behind a public network intermediary