When you trace the route your internet traffic takes from your device to a website server, you’ll pass through dozens of networks owned by different organizations. Each of those organizations is identified by an Autonomous System Number (ASN) — a unique identifier that plays a foundational role in how the internet is routed.
This article explains what an ASN is, who has one, how to look one up, and why it matters for understanding your own internet connection.
What Is an Autonomous System?
An Autonomous System (AS) is a collection of IP address ranges controlled by a single organization under a unified routing policy. Think of it as a country on the internet: it has its own territory (IP ranges), its own internal roads (internal routing), and border crossing rules (how it connects to other networks).
Examples of autonomous systems include:
- Google (AS15169) — controls the IP ranges used by Search, Gmail, YouTube, and Google Cloud
- Cloudflare (AS13335) — controls the ranges used by its CDN, 1.1.1.1 DNS, and security products
- Comcast (AS7922) — controls the IP ranges assigned to its residential broadband customers
- Your local ISP — almost certainly has its own ASN
What Is an ASN?
An ASN is the unique number assigned to an Autonomous System. They come in two formats:
- 16-bit ASNs: Numbers from 1 to 65,535 (the original format)
- 32-bit ASNs: Numbers from 1 to 4,294,967,295 (extended format introduced as 16-bit space filled up)
ASNs are assigned by Regional Internet Registries (RIRs) — the same organizations that allocate IP addresses:
- ARIN — North America
- RIPE NCC — Europe, Middle East, Central Asia
- APNIC — Asia Pacific
- LACNIC — Latin America and Caribbean
- AFRINIC — Africa
How Do ASNs Work? BGP Explained Simply
ASNs are the foundation of BGP (Border Gateway Protocol) — the routing protocol that determines how traffic moves between autonomous systems across the global internet.
Every AS announces its IP prefixes to neighboring ASes via BGP. These announcements propagate across the internet so that every network knows how to reach every other network. When you visit a website, BGP determines the path your packets take through dozens of autonomous systems to reach the destination.
This is why the internet is sometimes called a “network of networks” — it’s thousands of independent ASes, each with their own IP space, connected via BGP peering agreements.
How to Look Up an ASN
You can look up the ASN for any IP address or domain using the ExamineIP WHOIS tool. Enter an IP address and the tool queries the relevant RIR’s RDAP database to return the network name, ASN, owner, country, and abuse contact.
For example, if you look up 8.8.8.8, you’ll see it belongs to AS15169 (Google LLC), registered with ARIN, located in the United States.
You can also check what ASN your own IP belongs to:
- Visit tools.examineip.com to find your current IP
- Paste that IP into the WHOIS lookup tool
- The result will show your ISP, ASN, and network block
Why Your ASN Matters
Your ISP Has an ASN
Every residential ISP — Comcast, AT&T, BT, Deutsche Telekom, Digi Romania — has at least one ASN. When websites look up your IP address, they see your ISP’s ASN, which tells them who provides your connection and roughly where you are located. This is part of how IP geolocation works.
Websites Use Your ASN for Fraud Detection
Many websites check whether your IP belongs to a residential ISP ASN, a data center ASN, or a known VPN provider’s ASN. If you’re connecting from a data center IP (common with VPNs), the site may flag your session or show a CAPTCHA. This is why some services block VPN users — they detect the ASN doesn’t match a residential provider.
BGP Hijacking
Because BGP relies on networks trusting each other’s announcements, it’s vulnerable to BGP hijacking — when an AS falsely announces ownership of IP ranges it doesn’t control, redirecting traffic through itself. This has caused notable internet outages and is an ongoing security challenge.
Tier 1, Tier 2, and Tier 3 Networks
ASes are often classified by their position in the internet hierarchy:
- Tier 1: Networks that peer with every other Tier 1 and never pay for transit. Examples: AT&T (AS7018), Lumen/Level 3 (AS3356), Telia (AS1299), Cogent (AS174). They form the internet backbone.
- Tier 2: Networks that peer with some networks for free but pay Tier 1 providers for global reach. Most large ISPs and national telecom companies.
- Tier 3: Networks that only purchase transit — they pay upstream providers for all their connectivity. Most small ISPs and businesses with their own ASN.
Famous ASNs Worth Knowing
- AS15169 — Google LLC (includes 8.8.8.8 DNS)
- AS13335 — Cloudflare (includes 1.1.1.1 DNS, massive CDN)
- AS8075 — Microsoft (Azure, Office 365, Teams)
- AS14618 — Amazon AWS (largest cloud provider by IP count)
- AS32934 — Meta (Facebook, Instagram, WhatsApp)
- AS714 — Apple (owns the entire 17.0.0.0/8 block)
- AS6939 — Hurricane Electric (runs bgp.he.net lookup tool)
See full details on each of these networks in the ExamineIP ISP & ASN directory.
Your ISP can see your browsing activity via their ASN
A VPN encrypts your traffic before it reaches your ISP’s network, hiding the domains you visit. Try PureVPN or IPVanish.
Frequently Asked Questions
Can I get my own ASN?
Yes, but it requires a legitimate need (usually running a network that connects to multiple upstream providers), an application to your regional RIR, and a fee. Most individuals and small businesses don’t need their own ASN — they use their ISP’s.
Is an ASN the same as an IP address?
No. An ASN identifies an organization and its routing policy. An IP address identifies a specific device or interface. One ASN can cover millions of IP addresses.
Why does my IP show a different company than my ISP?
Some ISPs resell bandwidth from larger carriers, meaning the ASN lookup shows the upstream carrier rather than your retail ISP. This is also why IP location can be inaccurate — the IP might be registered to a carrier’s headquarters city, not your actual location.