Instantly retrieve detailed information about any Autonomous System Number (ASN), including organization, registry, and contact details.
An Autonomous System Number (ASN) is a unique identifier globally available for identifying an Autonomous System (AS). An AS is a group of IP networks that have a single, clearly defined routing policy.
ASNs are crucial for Border Gateway Protocol (BGP) routing, allowing different networks on the internet to communicate and exchange information.
Use our Reverse IP Lookup or IP WHOIS tool for granular IP-level details.
An ASN (Autonomous System Number) WHOIS Lookup is a specialized network utility that allows you to retrieve detailed registration information about a specific Autonomous System. Every major network on the internet—whether it's an ISP, a university, or a large tech company—is assigned a unique ASN to manage its routing. Correctly identifying ASN details is crucial for network administrators, cybersecurity analysts, and IT professionals who need to map network infrastructure or investigate connectivity issues.
Get immediate access to WHOIS data including owner name, registration country, and allocated IP prefixes.
We query authoritative regional internet registries (RIRs) like ARIN, RIPE, and APNIC for the most accurate information.
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The internet is essentially a "network of networks." These individual networks are known as Autonomous Systems (AS). Each AS is a collection of IP networks and routers under the control of a single organization that presents a common routing policy to the internet.
ASNs are critical for the Border Gateway Protocol (BGP), which is the system used to route data between these networks. Without unique ASNs, global routing would be impossible. By using our lookup tool, you can peel back the layers of internet infrastructure to see exactly who is responsible for a particular slice of the network.
Finding an ASN via the command line is a quick way for network engineers to verify routing paths.
whois -h whois.cymru.com <IP>.dig +short -x <IP> | awk '{print $1}' to reverse lookup.Reference: Team Cymru IP to ASN Mapping
The original ASN specification provided a 16-bit field, allowing for 65,536 unique numbers. As the internet expanded, this pool became insufficient.
32-bit ASNs were introduced to expand the pool to over 4 billion numbers. They are often written in:
Source: RFC 6793 (BGP Support for Four-Octet AS Number Space)
These errors are almost always related to Rate Limiting.
To prevent abuse, public WHOIS servers (like ARIN, RIPE, APNIC) impose limits on the number of queries allowed from a single IP address per minute/hour.
Just like private IP addresses (e.g., 192.168.x.x), there are Private ASNs intended for internal use within a large network topology (like a data center or campus). They should never appear on the public internet.
| Type | Range |
|---|---|
| 16-bit Private | 64512 - 65534 |
| 32-bit Private | 4200000000 - 4294967294 |
Reference: IANA ASN Registry
Resource Public Key Infrastructure (RPKI) consistently validates BGP route announcements. By using Route Origin Authorizations (ROAs), network operators can cryptographically certify which ASN is authorized to announce their prefixes, reducing BGP hijacking risks.
If a malicious actor tries to hijack the IP prefix (BGP Hijacking), routers performing RPKI validation will see the announcement as Invalid and drop it, securing the global routing table.
Yes, large organizations often own multiple ASNs for redundancy, load balancing, or administrative separation (e.g., separate ASNs for mobile vs. broadband networks, or different geographic regions).
This status means the ASN has not been assigned to any entity by IANA or the regional RIR.
It could be a number that has never been used, or one that was returned to the pool (deregistered) after a company closed or consolidated networks. These ASNs are held by IANA or the regional RIR until they are assigned to a new applicant.
Our lookup tool provides the 'Abuse Contact' email registered with the RIR (e.g., abuse-c in RIPE).
When you run a lookup on our tool, look for the "Contact Information" section. This email address is specifically designated for reporting:
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