ASN Lookup
Currently supports IPv4 addresses only.
About the ASN Lookup
An ASN Lookup identifies the Autonomous System Number and the organization responsible for a given IP address. An Autonomous System is a collection of IP networks managed under a single administrative entity, such as an ISP, a cloud provider, a university, or a large enterprise, and each one is assigned a globally unique ASN by a regional internet registry. The lookup maps an IP back to the network that announces it, telling you who actually operates the address space.
The tool works by consulting routing and registry data that associates IP prefixes with their originating ASNs. Internet routing relies on the Border Gateway Protocol (BGP), where each Autonomous System advertises the IP ranges it controls. By matching your queried IP against these BGP announcements and registry records, the lookup returns the AS number, the organization name, the country, and often the specific prefix the address falls within. This connects a single address to the larger block and the entity that owns it.
Common use cases include identifying the hosting provider or ISP behind an IP address, investigating the source of suspicious traffic or abuse, and verifying which network a cloud workload is actually running on. Security analysts use ASN data to recognize whether traffic originates from a residential ISP, a data center, or a known cloud platform, which informs risk scoring. Researchers and engineers also use it to understand peering relationships and the topology of the internet.
To dig deeper after an ASN Lookup, pair it with a WHOIS lookup to retrieve detailed registration and contact information for the address block, an IP Geolocation tool to estimate physical location, and a Reverse DNS check to find any hostname associated with the IP. Remember that ASN ownership reflects who routes the address, which may differ from who is actively using it, such as a customer leasing space from a hosting company.
Frequently asked questions
- What is an Autonomous System Number?
- An ASN is a globally unique identifier assigned to an Autonomous System, which is a network or group of networks operated under a single administrative policy. ASNs are used by the BGP routing protocol so networks can advertise which IP ranges they control.
- How is an ASN lookup different from a WHOIS lookup?
- An ASN lookup focuses on the routing layer, telling you which Autonomous System announces an IP and the operating organization. A WHOIS lookup returns registration details such as the allocated block, registry, and administrative contacts. They complement each other.
- Can the ASN tell me who is actually using an IP address?
- It tells you who routes the address, which is often a hosting provider or ISP. The actual end user may be a customer leasing that space, so the organization name reflects the network operator rather than necessarily the individual or company using the specific address.
- Why does the same organization sometimes have multiple ASNs?
- Large operators frequently hold several ASNs for different regions, business units, or networks acquired through mergers. Each Autonomous System represents a distinct routing policy domain, so a single company may legitimately announce its address space under more than one AS number.