ASN Lookup
Enter an AS number to see who holds it, every IPv4 and IPv6 prefix it announces with its RPKI status, where its address space is and its registry record. Enter an IP address instead to find the AS that announces it.
How AS numbers work
An autonomous system is a network that sets its own routing policy on the internet: an ISP, a cloud or hosting provider, a large company or a university. Each one has a number, assigned by the regional internet registry that serves it, and announces the address prefixes it routes over BGP under that number. The AS at the end of a route is its origin, and that's the AS an address belongs to.
AS numbers began as 16 bits, up to 65,535. Four-byte numbers, assigned since 2007, run to 4,294,967,295, and are written the same way: AS13335, AS398324.
Some numbers never appear in a route on the public internet: 64512 to 65534 and 4200000000 to 4294967294 are for private use, 64496 to 64511 and 65536 to 65551 for documentation, and AS0 and AS23456 have special roles. Bogon ASN lists every such range, free with an account.
What an AS page shows
Every AS has a page at its number, like AS13335. It opens with who holds the number, the registry that assigned it and when, and how many IPv4 addresses and IPv4 and IPv6 prefixes it announces. Below that are the share of its routes that are RPKI-valid, where its IPv4 space is by country, its registry record, every prefix it announces, and what each of our address-keyed databases holds in its space.
The pages read the current builds of ASN, BGP Route, ASN Whois and IP Geolocation. To name the AS of every address in your logs without a lookup each, IP ASN maps all announced space to its origin AS, and ASN gives every number's holder and type. Both are free with an account. ASN Extended adds each AS's upstreams, peers and downstreams.
Test the real build first.
An evaluation license puts a full current build in your hands, with no sampling, so you can measure it against your own traffic before anyone talks about terms.