ASN Lookup
Look up any autonomous system by number, IP address or organisation name: holder, country, all announced IPv4 and IPv6 prefixes, upstream and downstream networks, routing visibility and PeeringDB profile.
What an autonomous system is
The internet is a network of networks. Each independently operated network, an ISP, a cloud provider, a university, a large company, is an autonomous system with its own number. AS numbers are how routers know who announces which address ranges and through whom traffic should flow.
This lookup shows the holder of a number, every prefix it announces, the networks it buys transit from, the customers it serves and how widely the announcements are visible worldwide. Enter an IP address to find the AS that announces it, or a name to search the registry.
What you'll see
- Holder and registry: the organisation name and the regional registry that allocated the number.
- Announced prefixes: all IPv4 and IPv6 ranges currently originated by this AS, with the total number of IPv4 addresses.
- Upstreams: networks that carry this AS to the rest of the internet. Downstreams: networks that reach the internet through it.
- Visibility: how many route collectors see the announcements, and when the AS first appeared in routing tables.
- PeeringDB profile: self-reported network type, traffic level, peering policy and website, where the operator maintains one.
When it's useful
- Finding all address ranges of a provider to build firewall rules or allow lists.
- Understanding who is behind an address seen in logs, beyond the single IP.
- Checking the upstream dependencies of your own network or a supplier.
- Judging whether an address belongs to a residential ISP or a hosting company.