ASN Lookup
Look up an Autonomous System Number (ASN) to find its organization, country, total IP count, and announced IP ranges.
Enter an Autonomous System Number above to look up its details and IP ranges.
What Is an ASN?
An Autonomous System Number (ASN) is a unique identifier assigned to a network or collection of networks that operate under a single administrative domain and share a common routing policy. Every organization that connects to the internet through BGP (Border Gateway Protocol) — the protocol that routes traffic between networks — needs an ASN. Internet Service Providers, cloud hosting companies, large enterprises, content delivery networks, and universities all operate autonomous systems.
ASNs are allocated by Regional Internet Registries (RIRs): ARIN for North America, RIPE NCC for Europe and the Middle East, APNIC for Asia-Pacific, LACNIC for Latin America, and AFRINIC for Africa. Originally, ASNs were 16-bit numbers (ranging from 1 to 65,535), but as the internet grew, 32-bit ASNs were introduced (RFC 6793), extending the range to over 4 billion. 16-bit ASNs are still in widespread use, and most well-known networks have ASNs in the lower range. For example, Cloudflare is AS13335, Google is AS15169, and Amazon is AS16509.
Each autonomous system announces one or more IP address prefixes via BGP, telling the rest of the internet which IP addresses can be reached through that network. These BGP announcements form the global routing table — a constantly updated map of how to reach every publicly routable IP address. When you send a packet to a destination IP, routers use the BGP routing table to determine the path through multiple autonomous systems to reach the destination. This lookup tool queries BGP routing data to show you all the IP prefixes announced by a given ASN, along with the organization name, country of registration, and total IP address count.
ASN Use Cases
Network analysis and security research are primary use cases for ASN data. Security teams use ASN lookups to determine which organization controls a suspicious IP address, identify the hosting provider behind an attack, or map the network infrastructure of a threat actor. Correlating IP addresses with their ASN reveals patterns — for example, if all scanning traffic originates from a single ASN, it suggests a coordinated campaign rather than distributed noise. Threat intelligence platforms routinely enrich IP indicators with ASN data to provide context.
ISP identification and peering research rely heavily on ASN data. Network engineers use ASN lookups to identify potential peering partners, analyze traffic routing paths, and troubleshoot connectivity issues. Content delivery networks use ASN data to optimize traffic routing and ensure content is served from the nearest edge server. Internet measurement researchers study ASN-level topology to understand how the internet is structured and how traffic flows between major networks. ASN data is also used in geolocation, as the country and organization associated with an ASN provide a baseline location estimate for all IP addresses within that network.
Compliance and due diligence teams use ASN lookups to verify the network identity of business partners, investigate the hosting infrastructure of websites, and ensure that IP resources are legitimately allocated. Some regulatory frameworks require businesses to know which networks they interact with, making ASN lookups a standard part of vendor assessment.
To look up the geolocation of a specific IP within an ASN's address space, use our IP geolocation lookup. To calculate the size and details of any CIDR prefix announced by an ASN, try the CIDR calculator. For domain registration details of the organization behind an ASN, use our WHOIS lookup.