ASN Lookup

What is an ASN (Autonomous System Number)?

An Autonomous System Number (ASN) is a unique identifier assigned to a network—or a group of networks—managed under one administrative policy. On the public internet, Autonomous Systems exchange reachability information using BGP (Border Gateway Protocol). When you run an ASN lookup, you are asking: “Who operates this network on the internet routing graph?” For a full beginner guide, read What Is an ASN? in our Learn section.

ISPs, cloud providers, CDNs, universities, and large enterprises typically each have one or more ASNs. Famous examples include AS15169 (Google), AS13335 (Cloudflare), and many carrier ASNs that carry transit traffic worldwide.

ASN lookup by number vs by IP

You can look up an Autonomous System in two common ways:

• By ASN — enter AS15169 or 15169 to see organization, registry, and network details for that system.
• By IP address — enter a public IP such as 8.8.8.8. The tool resolves which ASN announces (or is associated with) that address so you can identify the network operator behind an IP you saw in logs, email headers, or firewall alerts.

How to use this free ASN lookup tool

1. Enter an ASN (with or without the AS prefix) or a public IPv4/IPv6 address.
2. Click Lookup ASN (complete the human check if shown).
3. Review organization name, country, registry, description, prefixes, and peer ASNs.
4. Continue with WHOIS, blacklist, or geolocation if you are investigating a specific IP.

How to read ASN lookup results

• ASN — numeric identifier (often written as AS####).
• Organization — entity that operates the Autonomous System.
• Country / registry — where the ASN is registered and which RIR issued it (ARIN, RIPE, etc.).
• Prefixes — IP ranges associated with the AS (what networks it can announce).
• Peers — neighboring ASNs that exchange traffic; useful for understanding connectivity.

ASN data is operational and registry-oriented. It does not identify a person at a home address. For abuse cases, combine ASN context with WHOIS abuse contacts and your provider’s reporting process.

ASN vs IP WHOIS vs geolocation

These tools answer different questions:

• ASN lookup — which network system routes or owns the routing policy for ranges?
• IP WHOIS — registry ownership and contacts for an IP block?
• IP geolocation — approximate city/region for an IP?

Network operators and security teams often run all three: ASN for routing identity, WHOIS for contacts, and geolocation for rough location context.

Public vs private ASNs

Public ASNs are unique on the global internet and required when you multi-home or advertise prefixes with BGP to external peers. Private ASNs (for example the 16-bit private range 64512–65534) are intended for internal use or private interconnects and should not be advertised to the global routing table. If you only need internal routing between your sites, a private ASN may be enough; if you need unique internet routing identity, request a public ASN through your RIR.

Common use cases for autonomous system lookup

• Identify which provider or company originates traffic from an IP in your logs
• Map CDN or cloud ranges (for allowlists, firewalls, or performance debugging)
• Understand peering and transit relationships at a high level
• Support abuse investigations with network-operator context
• Teach networking fundamentals (BGP, ASNs, prefixes) with real examples

Popular ASN examples

• AS15169 — Google LLC (includes well-known DNS such as 8.8.8.8)
• AS13335 — Cloudflare (includes 1.1.1.1 and large CDN space)
• AS36692 — OpenDNS / Cisco public DNS infrastructure

Use the example chips above the form to load these quickly, or pass a shareable link like /asn-lookup?asn=AS15169.