ASN Lookup

Look up an autonomous system number to see who operates the network and which addresses in it IPDebrief has profiled.

Try: 8.8.8.8 · 1.1.1.1 · 2001:4860:4860::8888 · AS15169

What an ASN is

The internet is a network of networks. Each independently routed network — an ISP, cloud provider, university or large company — is an autonomous system identified by an AS number. Autonomous systems announce the address ranges they route to their neighbours using BGP, and those announcements are how traffic finds its way across the internet.

AS numbers are allocated by the five regional internet registries. Originally 16-bit (1–65535), they are now 32-bit, so values above 4 billion are valid; ranges such as 64512–65534 are reserved for private use.

Why ASNs matter for security and networking

An ASN tells you who is responsible for an address, even when reverse DNS and registration data are vague.
Traffic from hosting ASNs is far more likely to be automated than traffic from residential ISPs.
Abuse often clusters in a handful of networks; ASN-level reputation helps spot it.
Network engineers use ASNs to debug routing, peering and route-origin validation.

Find the ASN for an IP address

Every IP profile shows the ASN that routes it. Enter an address in the IP lookup to get its ASN, then follow the link to the network's hub page. You can also browse the largest networks by number of profiled addresses.

Routing security and ASNs

Because BGP trusts what neighbours announce, a network can mistakenly or maliciously announce address space that belongs to someone else — a route hijack or route leak. Two defences tie address space to the ASNs allowed to originate it: RPKI route-origin authorizations, cryptographically signed by the address holder, and IRR route objects published in routing registries.

IPDebrief records the observed origin ASN for each profiled address together with route-origin validation status and route stability, so unexpected origin changes stand out. An address whose origin ASN changes frequently, or is announced without valid authorization, deserves extra scrutiny.

Frequently asked questions

How do I find the ASN of an IP?

Look up the IP address; its profile lists the originating ASN and links to the network page.

Can one organization have several ASNs?

Yes. Large providers often run separate ASNs per region, acquisition or service, and some ASNs announce space belonging to customers.

What is the difference between an ASN and an IP range?

An IP range is a block of addresses. An ASN is the network that announces and routes one or more such ranges.

Why does the ASN owner differ from the IP's registered owner?

Address blocks can be registered to one organization and routed by another, for example when a business uses addresses from its upstream provider or a cloud customer brings its own range.