The ASN Lookup tool allows you to query any Autonomous System Number to retrieve essential routing data, including the registered owner and associated IP prefixes. By entering an ASN, you can instantly inspect the network footprint and administrative details of a specific network operator on the global internet.
What is it
An Autonomous System Number (ASN) is a unique identifier assigned to a large network or group of IP networks that is controlled by a single administrative entity, such as an Internet Service Provider (ISP), enterprise organization, or hosting provider. Border Gateway Protocol (BGP) uses these numbers to exchange routing information across the global internet, ensuring that data packets find the most efficient path to their destination. The ASN Lookup tool queries authoritative registry databases to fetch the public metadata tied to a specific ASN, including the organization name, country of registration, and the complete list of IPv4 and IPv6 address blocks—known as prefixes—that the system originates into the global routing table. This gives you a clear, transparent view of how a network is structured and which IP spaces it controls.
Why it matters
Understanding the ownership and routing boundaries of IP addresses is critical for network administration, cybersecurity, and traffic engineering. When you encounter suspicious traffic hitting your firewall, performing an ASN lookup helps you quickly identify whether the traffic originates from a legitimate cloud provider, a known hosting service, or an unexpected foreign network. System administrators use this data to configure robust routing policies, implement precise BGP filtering, and construct geolocation or network-based access control lists (ACLs). If you are investigating a distributed denial-of-service (DDoS) attack or unauthorized scraping attempts, knowing the exact ASN helps you block entire blocks of malicious IP space efficiently. Furthermore, network engineers rely on these insights to verify that their own BGP announcements are propagating correctly and that upstream providers are advertising the intended IP prefixes.
How to use this tool
- Locate the input field on the ASN Lookup page.
- Type or paste the target Autonomous System Number into the box, ensuring you include the prefix if required (for example, entering
AS15169or simply15169). - Click the Check button to initiate the query against our network database.
- Review the generated report displayed on your screen, which details the organization, country, and announced IP prefixes.
How to read the results
When you query an active network, such as AS15169, the tool returns several key data points. The Organization Name field shows the legal registrant of the ASN, which might read "Google LLC". The Country field indicates the primary jurisdiction of the organization, typically represented by a two-letter ISO country code like "US". The Announced IPv4 Prefixes section lists all the IPv4 CIDR blocks originated by the AS, such as 8.8.8.0/24 and 8.8.4.0/24. Similarly, the Announced IPv6 Prefixes section displays the IPv6 address blocks, such as 2001:4860::/32. Reviewing these prefixes allows you to verify the exact scope of the network's visible footprint on the internet.
Common problems and how to fix them
Invalid ASN Format
Querying an incorrect string format, such as omitting the digits or including unsupported symbols, will result in a lookup failure. Ensure your input consists strictly of the numeric identifier or the standard "AS" prefix followed by the numbers.
Private or Reserved ASN
Private ASNs fall within specific reserved ranges (such as 64512 through 65534) and are used internally for routing within a private enterprise network rather than across the public internet. Querying a private ASN will yield no public registry data because these numbers are not routed globally.
Outdated Route Announcements
If the list of prefixes appears incomplete, it may be due to recent BGP updates that have not yet fully propagated across global routing tables, or the organization may be utilizing more specific sub-allocations managed through downstream providers.
Best practices
Always verify the ASN against multiple registries if you are performing forensic analysis on unfamiliar traffic. Combine ASN lookups with reverse DNS queries and IP geolocation checks to build a comprehensive profile of an unknown network actor. Keep your internal access control lists updated regularly, as organizations frequently acquire new IP blocks or spin up additional ASNs to manage their expanding global infrastructure.