IP Address Lookup
See which network an address belongs to, and who announces it.
What this tool does
Who announces it
The autonomous system and the organisation behind it — the authoritative answer to whose network an address is on.
Allocation detail
The prefix, the regional registry that allocated it and when.
Reverse DNS
The PTR name the address holder publishes, which often names the provider or the specific machine.
No geolocation guessing
City-level IP geolocation is inference and routinely wrong. Registry and routing data are facts, so that is what is shown.
Frequently asked questions
What does this tell me about an IP address?
Which autonomous system announces it, the organisation behind that AS, the prefix the address sits in, which regional registry allocated it and when, and the reverse DNS name if one is published. That is the routing and ownership picture, which is the durable, authoritative part.
Why does it not show a city?
Because IP geolocation is inference, not fact. It works by correlating registry data, latency and self-reported information, and it is routinely wrong at city level — particularly for mobile networks, VPNs and cloud addresses. Rather than present a guess as a location, this reports the registry and routing data, which is accurate.
What is an ASN?
An Autonomous System Number identifies a network that announces routes on the internet — an ISP, a hosting provider, a large enterprise. Every routable IP address belongs to a prefix announced by some AS, which makes the ASN the most reliable answer to "whose network is this".
Where does the data come from?
Team Cymru's IP-to-ASN service, queried over DNS. It is the same mechanism network operators use, it needs no API key or account, and nothing about the lookup is sent to a commercial data provider.
Can I look up a hostname instead?
Yes. A hostname is resolved to its first IPv4 address and that address is looked up. Note that a name behind a CDN resolves to the CDN edge, so you will see the CDN's network rather than the origin — which is the intended design.
Why does a private address return nothing?
Because ranges like 10.0.0.0/8 and 192.168.0.0/16 are not routable on the internet and belong to no autonomous system. There is nothing to look up, and the tool says so rather than showing an empty result that looks like a failure.
Monitor it, don't just check it
One-off checks catch what is broken today. CertNotify watches your certificates, domains, DNS and code continuously and tells you before something breaks.