ASN Lookup — Free & Instant

About this tool. Autonomous System Numbers identify the networks that make up the internet. Give us an IP and we'll tell you which AS announces it and who runs it; give us an ASN (like AS13335) and we'll show the operator's details.

Clear today is not the same as clear on Thursday.

Reputation attaches to networks as well as addresses, which is how a well-behaved sender on a bad neighbourhood ends up filtered anyway.

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How to read your ASN results

An ASN identifies an autonomous system, the network that routes a range of IPs. We show which network is behind an address.
Useful for spotting whether traffic comes from a cloud provider, an ISP, or a known bad network.

Common problems and how to fix them

You want to block a whole network

Identify its ASN here, then use your firewall or provider tools to filter that autonomous system rather than chasing individual IPs.

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Common questions.

What is an ASN?

An Autonomous System Number. It identifies a network that controls a set of IP routes on the internet.

How do I find the ASN for an IP?

Enter the IP here. We map it to the autonomous system that announces it.