ASN Lookup: a beginner's guide

An ASN (Autonomous System Number) is a unique number assigned to every "network" on the public internet. An autonomous system is a chunk of the internet that is run as a single administrative unit — a single ISP, a single big company's network, a single cloud provider, a single university. The internet is, structurally, a network of about 100,000 of these autonomous systems all exchanging traffic with each other through a routing protocol called BGP (Border Gateway Protocol). Every IP address on the public internet "belongs" to exactly one ASN, and the ASN is the answer to the question, "who actually runs the network this address sits on?"

You should care because the ASN is the most stable, useful identity an IP address has. Individual IPs change hands all the time (a hosting provider sells one to a customer, a customer migrates to a new ISP, a corporate office moves), but the ASN tells you the organization that controls the network. That is the answer to many practical questions: which cloud provider hosts this competitor? Which ISP serves my customers in Berlin? Is this attacking IP address coming from a residential network or a known bad-actor data center? Is the country a particular IP block is geolocated in actually consistent with the ASN's known coverage area?

The five things every ASN check looks at:

• The ASN itself. A number, e.g. `AS13335` (Cloudflare) or `AS15169` (Google).

• The organization name. Cloudflare, Google, Amazon, Microsoft, Comcast, BT, etc.

• The country of registration. The country the ASN was registered in (which may differ from where its IPs actually serve traffic).

• The IP prefixes (CIDR ranges) the ASN announces. Every ASN advertises a list of address blocks that belong to it.

• Peering relationships. Which other ASNs does this one exchange traffic with directly?

Three questions an ASN check answers:

• Who actually runs the network behind this IP address?

• For a sales call, is this prospect on AWS, Google Cloud, Azure, or somewhere more obscure?

• For an abuse investigation, which ISP do I need to contact to file a complaint?

The cost of skipping ASN data is making decisions about traffic without knowing who is responsible for it. The fix is one lookup per IP. ASNs and their underlying routing data are publicly available through services like bgp.he.net and the regional internet registries. The BGP protocol itself is defined in RFC 4271.

In one sentence: Get AS number, organization, and network type

Returns Autonomous System (AS) information for an IP (Internet Protocol address) address, including ASN (Autonomous System Number), organization name, country of registration, and network classification (ISP, hosting, enterprise). Covers 70+ major networks with AS type detection per the official internet standard (BGP-4) and the official internet standard (4-byte ASN).

Don't worry if some of the words above are still unfamiliar — there's a plain-language glossary at the bottom of this page, and most of the terms link to their own beginner guides if you want to learn more.

Here's what's actually happening behind the scenes when you call this endpoint:

Identifies the Autonomous System Number (ASN) responsible for routing traffic for an IP (Internet Protocol address) address. Returns the AS number, AS name (e.g., CLOUDFLARENET), organization (e.g., Cloudflare, Inc.), registration country, and network type classification (ISP, hosting provider, enterprise, education, or government). The response enriches Cloudflare's edge-level ASN data with a comprehensive database of 70+ major global networks, CDN (Content Delivery Network) providers, cloud platforms, and Tier-1 transit providers.

If you're using an AI assistant through MCP, you don't need to understand any of the technical details — the assistant calls the tool and translates the result for you.

Let's skip the marketing fluff and answer the only question that actually matters: why should you, a real human with a real to-do list, care about the ASN Lookup tool? Here's the plain-English version, written the way you'd hear it from a friend who happens to do this for a living.

ASN (Autonomous System Number) data reveals the organization behind an IP (Internet Protocol address) address, which is more reliable than reverse DNS (Domain Name System) or WHOIS (who is). It's essential for threat intelligence enrichment, abuse reporting, traffic segmentation, and understanding whether visitors come from residential ISPs, cloud hosting, or enterprise networks. Network type classification helps distinguish legitimate users from potential automated threats originating from hosting infrastructure.

Picture this in real life. Imagine a threat analyst. Here's the situation they're walking into: Enrich IOCs (Indicators of Compromise) with ASN (Autonomous System Number) data to identify malicious hosting providers, bulletproof hosters, and attacker infrastructure patterns across autonomous systems. Without the right tool, that person would be stuck copy-pasting between five browser tabs, reading documentation written for engineers, and crossing their fingers that the answer they cobble together is correct. With the ASN Lookup tool, the same person gets a clear answer in seconds — no spreadsheets, no guessing, no waiting for someone on the infrastructure team to free up.

Three questions this tool answers in plain English. If any of these have ever crossed your mind, the ASN Lookup tool is built for you:

• Where in the world is this server actually located, and who runs the network it sits on?

• How fast does traffic move between my users and my service?

• Is the IP address I am looking at part of a residential network, a data center, or something suspicious?

You can either click the tool and get the answer yourself, or ask your AI assistant — connected through MCP (Model Context Protocol) — to ask the question for you and translate the answer into something you can paste into Slack.

Who gets the most out of this. Network engineers, IT admins, sales teams qualifying enterprise prospects, and product teams building geo-personalization or fraud rules. If you see yourself in that list, this is one of the EdgeDNS tools you should bookmark today.

What happens if you skip this entirely. Skip it and you can't tell where your users actually are, who runs the network they're on, or why they're seeing slow page loads. That's why running this check — even once a month — is one of the cheapest forms of insurance you can give your domain.

If you're still on the fence about whether the ASN Lookup tool belongs in your toolbox, this section is for you. Below you'll meet three real people — a threat analyst, a security engineer, and a business intelligence — facing three real situations where this tool turns a stressful afternoon into a five-minute task. Read whichever story sounds closest to your week.

Story 1: Threat Intelligence Enrichment

Imagine you're a threat analyst. Enrich IOCs (Indicators of Compromise) with ASN (Autonomous System Number) data to identify malicious hosting providers, bulletproof hosters, and attacker infrastructure patterns across autonomous systems.

Why it matters: Build comprehensive threat profiles with network ownership context and identify clusters of malicious activity by ASN (Autonomous System Number).

Story 2: Bot & Fraud Detection

Imagine you're a security engineer. Classify traffic by ASN (Autonomous System Number) type to detect automated requests originating from hosting/cloud providers vs legitimate user traffic from residential ISPs.

Why it matters: Reduce false positives in bot detection by combining ASN (Autonomous System Number) type with behavioral signals.

Story 3: Traffic Analysis & Segmentation

Imagine you're a business intelligence. Analyze website traffic by ASN (Autonomous System Number) to identify visitor organizations (B2B enterprise visitors vs residential consumers vs cloud crawlers).

Why it matters: Segment traffic by organization type for account-based marketing, lead scoring, and accurate analytics.

Common situations across teams. Beyond the three stories above, here are the everyday workplace moments when people across the company reach for the ASN Lookup tool — or one of the tools right next to it in this category. If any of these are on your calendar this month, that's your sign:

• When a customer reports that your site is slow specifically from their region.

• When you need to know whether traffic is coming from a residential network or a data center.

• When planning a CDN, points of presence, or geographic expansion.

• During an outage, to see exactly where in the route packets are getting lost.

If you can see yourself in even one of those bullets, the ASN Lookup tool will pay for itself the first time you use it.

Still not sure? Here's the easiest test in the world. Open Claude, ChatGPT, Gemini, or any other AI assistant connected to the EdgeDNS MCP server and ask, in your own words: "Is the ASN Lookup tool useful for my job?" The assistant will look at the tool, ask you a couple of follow-up questions about what you're trying to accomplish, and give you a straight answer in plain English. No commitment, no signup forms, no jargon.

If you've connected the EdgeDNS MCP server to Claude, ChatGPT, Gemini, Cursor, or any other AI assistant, you don't need to write any code. Just ask in plain English:

"Use the ASN Lookup tool to check example.com and explain anything that looks wrong in plain language."

The AI will figure out which tool to call, fill in the right parameters, run it, and then explain the result back to you. No copy-pasting between tabs. No reading raw JSON. No memorizing endpoint names.

If you're a developer and want to call the endpoint from a script or your own application, here's the simplest possible example. Replace the placeholder API key with the real one from your dashboard.

There's just one piece of information you need to provide. The table below explains exactly what it is and what a real value looks like.

When you call this tool, you'll get back a JSON object with the fields below. If you're talking to it through an AI assistant, the assistant reads these for you and explains them in plain language — you don't need to memorize them.

These tools pair naturally with ASN Lookup. If you're already running this check, the related ones often answer the next question that comes up:

• IP Geolocation — Get location, ASN, and org for an IP

• Reverse DNS — Find hostname from IP via PTR lookup

• ASN Prefixes — Get all IPv4/IPv6 prefixes announced by an ASN

If you're using an AI assistant through MCP (Model Context Protocol), you can ask it to run several of these in one go: "Check ASN Lookup and the related tools for example.com and tell me what looks off."

If any words on this page felt like jargon, here's a plain-language version. Click any linked term to read a full beginner-friendly guide.

DNS (Domain Name System) — The internet's address book. When you type a website name, DNS turns it into the actual numeric address computers use to find each other.

IP (Internet Protocol address) — A unique number that identifies a computer on the internet, like a phone number for a server.

CDN (Content Delivery Network) — A worldwide network of servers that store copies of your website close to your visitors so pages load fast.

ASN (Autonomous System Number) — A unique number assigned to a big network operator (like an ISP or cloud provider). Tells you who owns a chunk of the internet.

WHOIS (who is) — A public record that tells you who registered a domain name, when, and through which company. Modern WHOIS is now called RDAP but most people still say 'WHOIS'.

RFC (Request for Comments) — The official internet standards documents. When someone says 'RFC 8484' they mean a specific numbered standards document — in that case, the one defining DNS over HTTPS.