Internet routing guide

What is an ASN?

Q: Why does an ASN matter?

An ASN helps explain which organization originates an IP address, which routed prefix covers it, and which registry or routing data source describes that network.

Q: Can an IP address move between ASNs?

Yes. Routing changes, transfers, provider changes, and hijacks can change the observed origin ASN for an IP prefix, so source labels and freshness matter.

What is an ASN? An autonomous system number identifies the network that announces a route on the public Internet, which is why it helps explain who operates the connection behind an IP address.

View an ASN lookup Open JSON example Check your connection

ASNAutonomous system number

RoutePrefix announced to the Internet

OriginThe AS currently seen announcing it

How ASN lookup helps

An IP address by itself tells you the address. ASN data adds routing context: the network organization, the covering prefix, the regional registry, and the source freshness behind the answer.

Use ASN lookup to identify the network behind an IP address or routed prefix.
Compare registry data with BGP-origin data when results are partial or stale.
Check source labels before treating routing data as current truth.

What WhatsMyConnection shows

The live lookup surfaces IP, prefix, ASN, domain, and MAC queries. ASN pages already show fixture-backed originated prefixes, source labels, warnings, and gated panels for richer public datasets when those runtime approvals are ready.

ASN FAQ

What is an ASN?

An ASN is an autonomous system number. It identifies a network or group of networks that announces routing information on the public Internet.

Why does an ASN matter?

An ASN helps connect an IP address to a network operator, routed prefix, registry, and observed BGP-origin data.

Can an IP address move between ASNs?

Yes. Provider changes, prefix transfers, routing policy changes, and routing incidents can change the observed origin ASN for a prefix.