Common questions about ASN assignment, organisation lookup, free access, and API usage.
What is an Autonomous System Number (ASN)?
An Autonomous System Number (ASN) is a globally unique identifier assigned to a network (or group of networks) that shares a single routing policy on the internet. Major ISPs, cloud providers, CDNs, and large enterprises each operate one or more ASNs to control how their IP traffic is routed via the Border Gateway Protocol (BGP).
What does an ASN WHOIS lookup return?
An ASN WHOIS lookup returns: the ASN number (e.g., AS15169), the organization name, the country of registration, the RIR that manages it, the IP prefixes (routes) announced by the ASN, creation and update dates, and abuse/technical contact information.
Why would I look up an ASN?
ASN lookups are commonly used by: network engineers (troubleshooting BGP routing issues), security analysts (attributing IPs to a specific cloud or hosting provider), threat intelligence teams (tracking malicious ASNs used by botnets or bulletproof hosters), and compliance teams (verifying approved network paths).
What is the difference between an ASN and an IP address?
An IP address identifies a single device or endpoint. An ASN identifies a network operator - the entity responsible for routing a block of IP addresses. One ASN typically covers thousands or millions of IP addresses.
How do I find the ASN for a specific IP address?
Use the IP WHOIS Lookup tool - it returns the originating ASN along with full IP block ownership data. Alternatively, tools like BGP.he.net can map an IP to its announcing ASN.
Can I look up all IP prefixes belonging to an ASN?
Yes. The ASN WHOIS result includes the list of IP prefixes (CIDR blocks) currently announced by the ASN, giving you visibility into the full IP footprint of that network operator.
Which organizations assign ASNs globally?
ASN assignment follows a two-tier system. IANA (Internet Assigned Numbers Authority) holds global authority over all Autonomous System Numbers and allocates them in blocks to five Regional Internet Registries (RIRs), which then assign individual ASNs to network operators and ISPs within their regions:
ARIN : North America
RIPE NCC : Europe, Russia & Middle East
APNIC : Asia Pacific
LACNIC : Latin America & Caribbean
AFRINIC : Africa
The RIR responsible for any ASN you look up is shown directly in the WhoisFreaks ASN WHOIS lookup result.
Is the ASN WHOIS lookup free to use?
Yes. Individual ASN lookups in the browser are completely free - no account required. Enter any AS number to instantly retrieve the owner, IP ranges, and network details. For users who need higher request volumes, bulk access, or the most current real-time data, paid API plans are available. Signing in also removes the data trimming applied to unauthenticated queries.
Can I access ASN data via API?
Yes. WhoisFreaks provides an ASN WHOIS API that returns owner details, IP prefixes, network ranges, and organization data in structured JSON. It is used by security teams for threat enrichment, network engineers for infrastructure monitoring, and OSINT researchers mapping an organization's full network footprint. Visit the API documentation to get started. New users receive free credits on signup.
What is the difference between ASN WHOIS and IP WHOIS?
IP WHOIS identifies who owns a specific IP address : it returns the registered organisation, ISP, ASN, abuse contact, and the IP range that address belongs to. This data comes from official Regional Internet Registry records.
ASN WHOIS goes one level up : it tells you about the autonomous system itself, the network entity that controls a group of IP ranges and announces them to the internet via BGP routing.
An IP address belongs to a range, and that range is managed by an ASN. So an IP WHOIS result will show you the ASN, and an ASN WHOIS result will show you all the IP prefixes that autonomous system controls.
Use IP WHOIS Lookup when you have a specific IP and want to know who is responsible for it. Use ASN WHOIS Lookup when you want to understand the full network infrastructure behind an organisation.
