Every network we've researched.

What an autonomous system actually is.

An autonomous system is a collection of IP networks operated under a single administrative authority and identified by a number, the ASN. Every organisation that connects to the internet in its own right holds one: internet providers, hosting companies, universities, government departments, banks, and large enterprises. When traffic leaves one network and crosses the internet, it passes from one autonomous system to the next until it arrives.

That is why AS numbers turn up in places you were not looking for them. A traceroute names one at every hop, and an abuse report cites the AS that originated the traffic. Most often it is a firewall log: a block of addresses you did not expect, and the question that always follows, which is who runs this and whether traffic from them is normal.

What each page contains

Every entry linked above has a page written from primary sources: observed BGP routing data for the prefixes the network originates, the IANA registry block the number sits in, and public documentation from the operator. A page sets out who holds the number, what the organisation does, which address blocks it was observed announcing, which networks it connects to, and what the address space is typically used for.

Where something cannot be verified, the page says so rather than filling the gap. Dormant and withdrawn registrations are described as dormant, not dressed up as active networks. A confidently wrong answer about who operates a network is worse than an honest gap, because the wrong answer is the one people act on.

Why these are grouped by role

Registry records describe network type in free text, and across this corpus that produces 793 distinct phrasings for what are really a handful of categories. government, u.s. federal government, and U.S. DoD all describe the same kind of operator. Those phrasings are normalised into the groups above so that related networks sit together.

Grouping by role also matches how people arrive. You rarely know an AS number in advance. You know you are looking at a hosting provider, a university network, or a government department, and what helps is seeing the others like it.

Related lookups

To look up a specific number rather than browse, use the ASN Explorer. To find the autonomous system behind an address you already have, start with the IP Lookup. For the address blocks themselves, the CIDR Calculator breaks a prefix down into ranges and host counts. If you are new to the topic, ASN explained covers the same ground at more length.