AS Lookup Tool
Understanding Autonomous Systems & Internet Routing
A guide to what autonomous systems are, how BGP routing connects them, and how to look up which organisation owns any IP address or ASN.
What Is an Autonomous System?
The internet is not a single network — it is a collection of tens of thousands of independently operated networks stitched together. Each of these networks is called an Autonomous System (AS).
An AS is a group of IP address ranges (called prefixes) and the routers that manage them, all under the control of a single organisation — an ISP, a cloud provider, a university, a government agency, or a large corporation. The defining characteristic is that the organisation presents a unified, consistent routing policy to the rest of the internet.
Every AS is assigned a globally unique Autonomous System Number (ASN). ASNs are either 16-bit (1–65535, the original range) or 32-bit (65536 and above, introduced as demand grew). You'll see them written as plain numbers (15169) or prefixed with AS (AS15169).
🌐 Well-Known ASNs
How Internet Routing Works
Autonomous systems don't operate in isolation — they exchange traffic with each other through a structured system of routing protocols and commercial agreements.
2.1 — BGP: The Routing Protocol of the Internet
Autonomous systems communicate with each other using BGP (Border Gateway Protocol) — the protocol that determines how traffic is routed across the public internet. BGP is often described as the "glue" that holds the internet together.
Each AS uses BGP to advertise which IP prefixes it can deliver traffic to. When a packet needs to travel from one AS to another, BGP determines the path — a sequence of ASes called the AS Path. Every significant latency jump in an MTR or traceroute result typically represents a handoff between two different autonomous systems.
ℹ BGP & Network Incidents
2.2 — IP Prefixes & AS Relationships
An AS doesn't announce individual IP addresses — it announces prefixes (blocks of addresses in CIDR notation). For example, Google announces 8.8.8.0/24, telling the internet to send any packet destined for that block to them.
| Relationship | Description |
|---|---|
| Peering | Two ASes exchange traffic directly at no cost — typically between similarly sized networks at internet exchange points (IXPs). |
| Transit | A smaller AS pays a larger AS (a transit provider) to carry its traffic to the rest of the internet. Most ISPs buy transit from a tier-1 provider. |
| Tier-1 | A small number of ASes that have full global reach purely through peering — they pay no one for transit. Examples: AT&T (AS7018), Lumen (AS3356), NTT (AS2914). |
⚡ Why This Matters for Performance
Regional Internet Registries
ASNs and IP address blocks are managed by five Regional Internet Registries (RIRs), each covering a geographic region. The Registry field in the tool result tells you which RIR allocated the ASN.
| Registry | Region | Coverage |
|---|---|---|
| ARIN | North America | United States, Canada, Caribbean |
| RIPE NCC | Europe & Middle East | Europe, Russia, Middle East, Central Asia |
| APNIC | Asia-Pacific | Asia, Oceania |
| LACNIC | Latin America | Latin America, Caribbean |
| AFRINIC | Africa | African continent |
ℹ Registry ≠ Server Location
What the Tool Returns
For any IP address or ASN, the tool returns the following fields from the RIR registration database.
The globally unique ASN (e.g. AS15169). Use this when referencing the network in BGP tools, RIR databases (whois), or routing table lookups.
Short handle registered with the RIR (e.g. GOOGLE). For large providers this matches the org name; for smaller ISPs or resellers they may differ.
Full legal name of the entity that owns the AS (e.g. Google LLC). This is the registered corporate name at the RIR.
Country where the AS is registered. Reflects corporate domicile, not the physical location of any specific server — a global CDN may register in one country while serving traffic worldwide.
The Regional Internet Registry that allocated the ASN: ARIN (North America), RIPE (Europe/Middle East), APNIC (Asia-Pacific), LACNIC (Latin America), AFRINIC (Africa).
Date the RIR assigned this ASN. Pre-2000 allocations typically belong to universities, legacy ISPs, or large early internet adopters.
How to Use This Tool
The tool accepts two types of input:
IP address
Enter any public IPv4 or IPv6 address (e.g. 8.8.8.8 or 2606:4700:4700::1111). The tool looks up which AS is responsible for routing that address and returns the full AS details.
AS number
Enter an ASN directly, with or without the prefix (e.g. AS15169 or 15169). The tool returns the registration details for that AS.
💡 Tip — Find Your Own ISP
Interpreting Results
A few fields in the results deserve extra attention when reading the output.
| Field | How to Read It |
|---|---|
| AS Number | The canonical identifier. Always prefixed with AS. Use this when cross-referencing in BGP tools or RIR whois databases. |
| Name vs Org | Name is the short RIR handle (e.g. GOOGLE). Organization is the full legal entity (e.g. Google LLC). For large providers they match; for smaller ISPs or resellers they often differ. |
| Country | Registration country, not server location. A global CDN registers in one country but serves traffic from hundreds of locations worldwide. |
| Allocated | Pre-2000 allocations belong to universities, legacy ISPs, or early internet adopters. Very recent allocations may be new entrants or reassigned blocks — worth noting for security analysis. |
⚠ Private & Reserved ASNs
Practical Use Cases
AS lookup is a foundational tool for network investigation. Here are the most common scenarios where it is useful.
Identify who owns an IP
Look up a suspicious IP to see which organisation registered it — ISP, cloud provider, hosting company, or VPN service.
Verify your VPN or proxy
Look up your public IP. If the AS is your VPN provider, the VPN is active. If it shows your ISP, traffic is going direct.
Diagnose routing issues
Cross-reference ASNs seen in MTR or traceroute results to identify exactly where in the network path a problem is occurring.
Security research
Identify the network origin of traffic hitting your infrastructure — bot farms, scanners, and proxies often cluster in specific ASes.
CDN / cloud validation
Confirm traffic is arriving from an expected provider — e.g. Cloudflare-proxied sites should show AS13335; AWS origins show AS16509.
Check geolocation accuracy
Compare the ASN's registered country against where you expect the server to be. Discrepancies explain why IP geolocation sometimes gets it wrong.