What is an ASN (Autonomous System Number)?

The internet is a network of networks. Each large network that runs its own routing, such as an internet provider, a mobile carrier, a university or a cloud company, is called an autonomous system and has a unique Autonomous System Number (ASN). Our IP Lookup shows the ASN of any address.

Examples

Your home provider has one too; the home page shows yours under "ASN".

How ASNs work

Autonomous systems exchange routes with each other using BGP (Border Gateway Protocol). Each network announces the IP address blocks it owns, tagged with its ASN. Routers around the world use these announcements to decide the path traffic takes. When you open a website, your traffic crosses several autonomous systems between your provider and the site.

ASNs are assigned by the five regional internet registries. Originally 16-bit numbers (up to 65,535), they have been 32-bit since 2007, allowing over four billion.

What an ASN tells you about an IP address

• Who runs the network: an internet provider, a hosting company, a business or a university.
• Whether it is a home or data-center connection. Traffic from cloud and hosting ASNs (AWS, DigitalOcean, OVH and others) is rarely a real person browsing, so many sites treat it like a VPN or bot. Our VPN & Proxy Check uses this signal.
• Which country the network is based in, which may differ from where an address is used.

ASN vs IP address

An ASN identifies a whole network; an IP address identifies one connection within it. Google's AS15169 announces millions of addresses. A small business may have one ASN with a few hundred addresses.

Frequently asked questions

Do I have my own ASN?

No. Home users share their provider's ASN. Organizations apply for their own ASN when they connect to several providers.

Can an ASN reveal who I am?

No. It identifies your provider, not you.

Why do VPN servers show a hosting ASN?

Most VPN providers rent servers in data centers, so their addresses belong to hosting networks.