An Autonomous System Number (ASN) is a globally unique identifier assigned to a network that controls its own routing policy on the internet via BGP (Border Gateway Protocol). Every major ISP, cloud provider, CDN, and large enterprise operates one or more ASNs. The ASN WHOIS Lookup retrieves the full registration record for any ASN — including the IP prefixes it announces, the organization that controls it, and its abuse contact information.
When troubleshooting BGP routing anomalies — route leaks, hijacks, or unexpected path changes — ASN WHOIS is the starting point. It confirms which organization is authoritative for an ASN, what prefixes they're supposed to announce, and who to contact if something is wrong. Pair with IP WHOIS Lookup to verify individual IP allocations within the AS.
Many threat actors operate or abuse specific ASNs — particularly bulletproof hosting providers that ignore abuse reports and knowingly host malicious infrastructure. Tracking malicious ASNs across campaigns is a core threat intel technique. Knowing the full IP prefix list of a suspect ASN lets analysts build comprehensive blocklists.
Organizations that need to restrict traffic by geographic region or network operator use ASN WHOIS to build accurate allowlists and blocklists. A single ASN lookup returns the complete list of IP prefixes announced by that AS — enabling precise firewall rules based on network operator rather than individual IPs.
Security teams use ASN lookups to map the complete IP footprint of cloud providers (AWS, Google, Cloudflare, Akamai) for network policy enforcement. Combine with our Reverse DNS Lookup to identify specific hostnames within those IP ranges.
Enter either the ASN number (e.g., AS15169) or just the number (15169) — WhoisFreaks handles both formats automatically.
