IP ASN Lookup
See which autonomous system announces an IP address, the prefix it belongs to, and the network name recorded by the regional registry.
Run IP ownership and ASN lookup
No sign-up required. Public hosts and addresses only; results show what was observed, nothing is simulated.
What an ASN lookup tells you
The internet is a collection of autonomous systems, each identified by an AS number, that announce blocks of addresses to each other using BGP. This tool takes an IP address, or a host name whose addresses it resolves, and reports the autonomous system that originates the covering route, the announced prefix, the allocation registry and country, and the network name from the registry's own records.
It is useful for answering practical questions. Is this server hosted at a cloud provider or inside a corporate network? Do two addresses belong to the same operator? Is a mail server sending from the provider you expect? Public IPv4 and IPv6 addresses are supported; private and reserved addresses are refused rather than queried.
Where the data comes from
The origin AS and prefix come from the Team Cymru IP-to-ASN mapping service, queried over DNS with TXT lookups. Team Cymru is a third-party public service. The network name is added from the RDAP record published by the regional internet registry that manages the address. Because the routing data belongs to an external provider, it can lag behind changes, and anyone planning high-volume or commercial use of such a service should confirm its terms.
RDAP coverage varies between registries and over time. Some registries return rich organisation names, others return only a handle, and a lookup that fails is reported as unknown, never as proof that an owner does not exist.
How to read the results
Each address produces a row with its AS number, AS name, announced prefix, registry and country.
- AS number and name: the network that originates the route. Customers of a hosting company share that company's AS, so the AS identifies the provider, not an individual tenant.
- Prefix: the announced block containing the address. Several addresses in one prefix are in the same routed network.
- Registry and country: where the block was allocated. This is an allocation record, not the physical location of the server.
- Network name: a label from the registry record, sometimes the customer, sometimes the upstream provider.
- No origin AS: the service has no route for the address in the data it uses. It may be unannounced or the data may be incomplete.
Common pitfalls
Anycast and CDN addresses are announced from many locations, so a single AS and country do not describe where a request is actually served. An address allocated to a company in one country can be used by a server in another. A shared hosting IP belongs to the provider's AS even though hundreds of unrelated sites use it.
Do not read an ASN as a verdict about trust or abuse. It says who announces the route; it says nothing about the behaviour of the service behind it.
Using the result safely
This is a read-only lookup with no change to make, but the information supports several safe actions. Use the provider name to find where a firewall or security-group change must be made. Use the prefix when writing an allow-list, but remember that prefixes can change, so avoid hard-coding a whole provider's ranges where the provider publishes its own list. Confirm that mail servers and sending services belong to the networks you expect before adding them to SPF.
- Run the lookup for the address you are investigating.
- Compare the AS name with the provider you believe hosts the service.
- If it differs, check for a CDN or proxy in front, using the reverse DNS and open-port tools.
- For allow-lists, prefer the provider's published ranges and review them on a schedule instead of freezing today's prefix.
Limits
The origin AS is derived from routing data as seen by the service; it is not proof of who operates a server. Country is the registry allocation country. The lookup covers addresses only, so it cannot tell you which organisation registered a domain name; use RDAP for that. If the third-party DNS service is unreachable the tool reports an unknown result instead of an empty one.
Frequently asked questions
Does the ASN show where the server is physically located?
No. It shows the network that announces the address. The country comes from registry allocation and may differ from the physical location.
Why do two unrelated sites show the same ASN?
They are hosted by the same provider. The AS belongs to the provider, and its customers share it.
Where does this data come from?
The Team Cymru IP-to-ASN mapping service over DNS, plus the regional registry's RDAP record for the network name. Both are third-party sources.
What does 'no origin AS' mean?
The mapping data has no route covering that address. It might be unannounced, newly announced or missing from the source.
Is a particular ASN trustworthy or malicious?
This tool does not rate ASNs. It reports ownership data only.
Can I look up a domain name?
Yes, as a convenience: the tool resolves the host's addresses and looks up each. For registration data of the domain itself use the RDAP lookup.
Scope of this tool
- Source: Team Cymru IP-to-ASN mapping service (DNS TXT at origin.asn.cymru.com / origin6.asn.cymru.com / asn.cymru.com), plus the regional registry's RDAP record for the network name. Team Cymru is a third-party public service; an owner who plans high-volume or commercial use should confirm its terms of use.
Written by DNS Tools editorial · Last updated 2026-10-09