Autonomous systems

The largest networks

Ranked by the prefixes the ASN database assigns to each system, both address families together. Each page lists the prefixes, the registry facts and the operator-level flags, and the same facts are one API call away.

catalog warmed 2026-09-12 · index built 2026-09-12

What an autonomous system tells you

An autonomous system number names the network an address is announced from, and the operator behind it is the most reliable fact about an address there is: a cloud, a carrier, a university or a hosting company each announce their own space. The IP lookup answers the number and the operator on every address; these pages turn that around and show every prefix a system holds, the registry that allocated it and when, and whether its operator is on Spamhaus ASN-DROP or a listed satellite or mobile network.

What none of this says is who is using an address today. A prefix belongs to its operator; a person behind a carrier gateway, a VPN exit or a corporate proxy is not the operator. Look up an address to see the flags that separate the two.

Common questions

What is an autonomous system number?

An ASN identifies one network that announces its own routes to the Internet under a single routing policy: a cloud, a carrier, a university, a hosting company. Every public IP address belongs to exactly one, which is why the number and the operator behind it are the first facts an IP lookup answers. The glossary entry explains how the number is read.

Why only the largest networks?

The index knows every system the ASN database assigns a prefix to, tens of thousands of them, and a page exists for each — but only the largest by prefix count are listed here and submitted for indexing. A network with one /24 does not need a search result; a link to its page still works.

Where do the prefixes come from?

From the free DB-IP ASN database turned inside out: the same file the lookup reads address by address is walked once a month to list every prefix per system. The registry, country and allocation date come from the regional registries’ own daily statistics, and the blocklist, satellite and mobile flags from the lists the lookup already uses. Nothing here is a live route table.