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What is an 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.
