Enter an IP address, a hostname or an AS number such as AS13335. For an IP or hostname you get the autonomous system that announces it, the BGP prefix, country and registry. For an AS number you get its name, the IPv4 and IPv6 prefixes it announces and its contacts.
Table of Contents
What an ASN tells you
An autonomous system is a network with its own routing policy, such as a hosting company, an ISP or a cloud provider, identified by an AS number. Knowing the AS behind an IP tells you who runs the network, which is useful for abuse reports, for spotting traffic from a hosting provider rather than a home connection and for checking that your own IPs are announced correctly.
IP to ASN
The lookup uses Team Cymru’s IP-to-ASN mapping, which reflects what BGP routers actually see. The prefix shown is the announced route that contains the IP, which can be larger or smaller than the block your provider assigned to you.
AS number lookup
For an AS number, the announced prefixes come from RIPEstat, based on routing data collected over the last two weeks, and the organisation and abuse contact come from RDAP. The first 40 IPv4 and 20 IPv6 prefixes are listed.
ASN Lookup at a glance
Official documentation: Team Cymru IP to ASN mapping, RIPEstat.
Related guides: Mail server IP blacklisted: delisting runbook · CSF AlmaLinux 10: nftables and ipset Problems Fixed.
Frequently asked questions
Why does my IP show my provider’s AS?
Most customers do not have their own AS. Your provider announces a larger block that contains your IP, so the provider’s AS is the correct answer.
What does not announced in BGP mean?
No route for the IP is visible on the internet, so it cannot be reached from outside. It may be unused, reserved or announced only inside a private network.
Can I block a whole AS in my firewall?
Yes, by blocking its announced prefixes, for example with an ipset in CSF or firewalld. Use it with care: large providers host both attackers and real visitors.