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ASN / Prefix Lookup

Map IP to ASN / origin, and list announced prefixes.

Data via Team Cymru DNS; no storage, no tracking.
Results will appear here…
Prefix discovery
IP lookups return origin prefix, country and ASN name if published.
ASN lookup
Query AS numbers directly (AS13335) to fetch the org name fast.
Privacy & freshness
Data is fetched live via DNS (Team Cymru); no results are stored.
Server-sideProcessed server-side

This tool uses a server-side service for processing; uploaded files or requests are not kept for long-term storage.

About

Use ASN lookup to understand which network an IP address belongs to. Instead of focusing on a single IP, ASN/prefix information tells you who announces the range on the internet (ISP, data center, cloud provider, or VPN).

This is useful for security and operations: allowlisting corporate networks, investigating suspicious traffic, or explaining why access differs between regions. ASN data also helps confirm whether traffic comes from a consumer ISP or a hosting provider.

Keep in mind that IP ownership and routing can change. Treat the results as a diagnostic signal and verify with authoritative sources if you’re making critical policy decisions.

How it works

  1. 1Open ASN / Prefix Lookup and choose your file or enter the required input.
  2. 2Check the settings and start the process.
  3. 3The tool creates the result with temporary server-side processing.
  4. 4Download the output or copy the result when it is ready.

FAQ

›What is an ASN?
An Autonomous System Number identifies a network on the internet that announces IP prefixes via BGP.
›What is a prefix?
A prefix is an IP range (CIDR) like 203.0.113.0/24. It represents a block of addresses announced together.
›Is ASN the same as ISP?
Often, but not always. A data center, cloud provider, or VPN can also have an ASN.
›Can I use ASN for allowlisting?
Some systems support ASN-based policies; otherwise, you typically allowlist specific prefixes or IPs.
›Does ASN show the exact location?
No. ASN is about network ownership/routing, not precise geolocation.