JA Technology Solutions
ASN Lookup
Look up ASN, AS name, announced prefix, country, and registry for any IPv4 or IPv6 address.
ASN Lookup
Given an IP address, this tool returns the Autonomous System Number (ASN), AS name and operator, the announced prefix (CIDR) the IP belongs to, the country of registration, the regional registry (ARIN, RIPE, APNIC, LACNIC, AFRINIC), and the allocation date. It uses Team Cymru's free DNS-based IP-to-ASN service — no API key required — via Cloudflare DoH, so queries run entirely in your browser.
Learn more ↓
Loading interactive explorer...
What an ASN Is
An Autonomous System Number (ASN) identifies a network that participates in BGP — the internet's inter-domain routing protocol. Every ISP, cloud provider, large enterprise, and university has one (or several). When a network wants to announce that it owns a particular block of IP addresses to the rest of the internet, it does so with a BGP announcement tagged with its ASN. Looking up an ASN for an IP tells you who is announcing that IP — which in practice is usually the same as who owns and operates it.
Why Team Cymru
Team Cymru is a non-profit security research organization that has operated a free DNS-based IP-to-ASN lookup service since 2005. The data comes from their BGP route collectors and reflects what networks are actually announcing globally. Unlike commercial IP intelligence APIs, there's no rate limit for casual use, no API key, and the format is stable (ASN | prefix | CC | registry | allocated). This tool wraps their service in a browser-friendly UI.
What You Can Do With It
ASN lookups are a core primitive for log enrichment (labeling traffic by the network it came from), security investigations (clustering related events by ASN), fraud detection (flagging traffic from ASNs associated with abuse), threat intelligence (enriching IOCs with network metadata), and cost allocation (seeing which cloud providers a workload is talking to). I've built ETL pipelines that incorporate ASN lookups for clients in adtech, finance, and security.
Multiple Origin ASNs
A single IP address can sometimes appear to be announced by multiple ASNs — this usually means the prefix is multi-homed (announced by more than one provider simultaneously), or there's an intentional or accidental BGP hijack in progress. When Team Cymru returns multiple ASNs for a prefix, this tool lists each one separately with its own card.
Need Custom Enrichment?
If you need ASN enrichment baked into your log pipelines, security stack, or fraud detection, I can help you build it. See ETL and data pipeline development, integration services, or get in touch.
All tools run entirely in your browser. Your data never leaves your machine. Need help? Ask James.