An autonomous system number identifies a network that routes its own IP space on the internet.

Why does this matter for email?

Reputation systems often judge senders by network as well as by single IP.

ASN Lookup

An autonomous system number (ASN) identifies the network, such as an ISP, cloud, or hosting company, that announces an IP address range on the internet. This lookup finds the ASN, prefix, country, and registry for an IP.

When to use this: You want to know which provider or network an IP address belongs to. Command prefix asn:

About the ASN Lookup

Find the autonomous system (network) that announces an IP address, with its prefix, country and registry.

FAQ

What is an ASN?: An autonomous system number identifies a network that routes its own IP space on the internet.
Why does this matter for email?: Reputation systems often judge senders by network as well as by single IP.