Look up an Autonomous System Number to see the organisation and all announced IP prefixes. Also resolves any IP address to its ASN.
Enter an AS number or IP address to look up
An Autonomous System Number (ASN) is a unique identifier assigned to a network or group of networks under a single administrative policy - typically an ISP, a large enterprise, a CDN, or a cloud provider. Each AS exchanges routing information with other ASes using BGP (Border Gateway Protocol), the protocol that determines how traffic flows across the internet.
An AS "announces" the IP address ranges (prefixes) it is responsible for to its neighbours via BGP. A prefix like 104.16.0.0/13 tells the internet that traffic destined for those IPs should be routed to that AS. The list of announced prefixes is what this tool shows - sourced from RIPE NCC's routing registry, updated in near real-time.
ASN lookups are useful for: identifying who owns an IP block (for abuse reports or security investigations), verifying BGP routing for your own infrastructure, checking whether an IP is part of a known CDN or cloud provider, and auditing which IP ranges belong to a specific organisation.
Enter any IP address and the tool performs a reverse lookup to find which AS announces the prefix that contains it. This is done via RIPE NCC's routing data. The result shows the containing ASN and then loads the full AS details. Note that some IPs may be in prefixes announced by multiple ASes - the tool returns the most specific (longest prefix match).