How to use the asn lookup
- Type the AS number with or without the AS prefix and press Look up.
- Read the name and country from the routing data, then the organisation and dates from the registry record.
- Follow the link to the IP Lookup if you started from an address and want to confirm which AS announces it.
Features
- Accepts AS13335, as13335, AS 13335 or a bare number
- AS name, registry country, RIR and allocation date from Team Cymru's DNS-based service
- RDAP autnum record: holding organisation, handle, block range when the number is part of a larger allocation, registration and update dates
- Private, reserved and documentation ranges recognised and explained instead of queried
- Copyable plain-text report
What an AS number is
The internet is a network of networks. Each independently operated network that exchanges routes with others, such as an ISP, a cloud provider, a CDN, a university or a large enterprise, is an autonomous system, identified by a number. Routers use these numbers in BGP to describe the path a packet's destination is reachable through. When you see 'origin AS' next to an address, it is the network that announced the block containing that address.
Numbers up to 65535 are the original 16-bit range; larger ones are 32-bit numbers introduced as the small range ran out. 64512–65534 and 4200000000–4294967294 are private, used inside organisations and never seen on the public internet.
Two sources, two views
The routing view comes from Team Cymru, which derives it from the global BGP table, so it reflects what the network is called in routing databases. The registry view comes from the regional registry (ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC) through RDAP, the modern replacement for WHOIS, and shows the legal holder. They usually agree; when they differ it is normally because the registry name is the parent company and the routing name is a brand or subsidiary.