By: Katia Belokon · Updated June 2026
What is an Autonomous System Number (ASN)?
An Autonomous System Number (ASN) is a globally unique number assigned to a network operator that independently controls a set of IP address prefixes and exchanges routing information with other networks using the Border Gateway Protocol (BGP). The term "autonomous system" refers to the network itself — the collection of IP ranges under one administrative control.
Common examples of network operators with their own ASNs include internet service providers (ISPs), cloud providers, content delivery networks (CDNs), large universities, and major corporations. For example:
- AS13335 — Cloudflare Inc. (CDN, 1.1.1.1 DNS resolver)
- AS15169 — Google LLC (Google Cloud, 8.8.8.8 DNS)
- AS16509 — Amazon.com Inc. (AWS)
- AS9009 — M247 Europe (widely used by commercial VPN providers)
- AS394711 — Mullvad VPN AB (Mullvad's own infrastructure)
How do ASNs work?
ASNs are used in the Border Gateway Protocol (BGP), the routing protocol that connects the internet's networks. Each autonomous system announces the IP prefixes it controls to its neighboring ASes. Routers then use these announcements to build routing tables that determine how to forward packets from any point on the internet to any other point.
When you visit a website, your request travels through a chain of autonomous systems — starting from your ISP's ASN, through transit providers, and arriving at the ASN that hosts the destination server. Every hop between autonomous systems is governed by BGP.
ASNs were originally 16-bit numbers (range 1–65535). In 2007, 32-bit ASNs were introduced to expand the available pool. Numbers 64512–65534 are reserved for private use, similar to private IP address ranges.
How to look up an ASN
When you run an IP lookup on MyIPScan, the result includes an ASN field that identifies the network operator controlling that IP address. For example, if your visible IP is 104.16.132.229, the ASN lookup will return AS13335 (Cloudflare). This tells you the traffic is routing through Cloudflare's infrastructure.
You can look up an ASN directly using MyIPScan's IP Geolocation Lookup or WHOIS Lookup tools. External resources such as bgp.he.net also allow you to view all IP prefixes advertised by a given ASN.
Why your visible ASN changes when you use a VPN
When you connect to a VPN, your outbound internet traffic exits through the VPN server's IP address rather than your ISP's gateway. This causes your visible IP address and associated ASN to change to those of the VPN provider or its hosting partner.
For example, if you use Mullvad VPN and your traffic exits through one of Mullvad's own servers, your visible ASN will be AS394711 (Mullvad VPN AB). If you use NordVPN and your exit node is hosted on M247, your visible ASN will be AS9009 (M247 Europe).
If an IP lookup while connected to a VPN still shows your real ISP's ASN, this may indicate a VPN IP leak — your traffic is bypassing the VPN tunnel and exiting through your ISP. Use the VPN Leak Test to check for this.
What common ASNs mean in privacy tests
When you see an unexpected ASN in a DNS leak test or VPN test, it helps to know what type of network that ASN belongs to:
- Your ISP's ASN appearing while connected to a VPN — possible IP or DNS leak. Run the VPN Leak Test.
- Cloudflare (AS13335) in a DNS test — you are using Cloudflare's 1.1.1.1 DNS resolver, either directly or through your VPN.
- Google (AS15169) in a DNS test — you are using Google's 8.8.8.8 DNS resolver.
- M247 (AS9009) as your exit IP — common when using ExpressVPN, NordVPN, or other commercial VPNs that use M247 hosting.
- Mullvad (AS394711) as your exit IP — confirms your VPN exit is through Mullvad's own infrastructure.
Browse the full ASN lookup index for context on 40 major Autonomous Systems.
Frequently asked questions
What does ASN stand for?
ASN stands for Autonomous System Number. It is a globally unique number assigned by regional internet registries (RIRs) to a network operator that independently controls a set of IP address prefixes.
Who assigns ASNs?
ASNs are assigned by Regional Internet Registries (RIRs): ARIN (North America), RIPE NCC (Europe, Middle East, Central Asia), APNIC (Asia-Pacific), LACNIC (Latin America), and AFRINIC (Africa). Overall coordination is managed by IANA.
Why does my visible ASN change when I use a VPN?
When you connect to a VPN, your outbound traffic exits through the VPN server rather than your ISP. Your visible IP and ASN change to those of the VPN or its hosting provider. If your real ISP's ASN still shows while connected to a VPN, this indicates a VPN leak.
How many ASNs exist?
As of 2026, approximately 100,000 active ASNs exist globally. ASN numbers were originally 16-bit (1–65535) and extended to 32-bit to accommodate growth. Numbers 64512–65534 are reserved for private use.
What is the difference between an IP address and an ASN?
An IP address is a specific address assigned to a device or server. An ASN identifies the network operator controlling a block of IP addresses. One ASN can cover millions of IPs. For example, AS13335 (Cloudflare) includes 1.1.1.1 and millions of other IPs across its CDN and DNS infrastructure.