IP / ASN Lookup
Look up an IP's owning org, ASN and allocation via RDAP.
IP ASN Lookup checks, in real time, which Autonomous System (AS) an IPv4 address belongs to and which IP prefix (CIDR block) it is advertised under on the internet. It shows the ASN, the owning organization (holder) and the prefix at a glance, so you can quickly tell which ISP, cloud or hosting provider's network an address sits in.
Lookups are based on public routing data published by the RIPE NCC (RIPEstat), and results are briefly cached for speed. It is handy for tracing the origin of an IP in your server logs, identifying the source network of abusive traffic, or verifying that your own ranges are advertised under the correct ASN. For the IP's rough location, pair it with IP Geolocation; to find a domain's IP first, use Website IP Lookup.
What is an ASN?
An Autonomous System Number is a unique identifier assigned to a group of IP networks operated under a single routing policy (an autonomous system). ISPs, cloud providers and large enterprises each hold one or more ASNs and exchange routes with each other over BGP. Looking up an IP's ASN and holder tells you which organization's network the address belongs to.
What is an IP prefix (CIDR)?
A prefix is the contiguous block of IP addresses that an ASN advertises on the internet, written in CIDR notation such as 203.0.113.0/24. It shows which range a single input IP is actually routed as part of.
How to read the results
- ASN: the autonomous system number advertising the IP
- Holder: the organization registered for that ASN
- Prefix: the advertised CIDR range containing the input IP
If more than one ASN is shown for a single IP, it may be advertised from multiple origins (MOAS) or reflect a difference in the data snapshot.