Choosing an ASN Lookup Input
Enter an AS number such as AS15169 to retrieve its registration, an IP address to find its routing origin, or a domain name to inspect the addresses returned by DNS. These inputs follow different paths through the lookup. A direct AS number query does not first resolve a domain or search for an IP address.
You can enter an AS number with the AS prefix or as a decimal number. IPv4 and IPv6 addresses are both supported. Enter a single address rather than a CIDR block: this form does not enumerate every address in a subnet. The input summary confirms the interpreted query type and normalized value.
For a web address, the lookup extracts the host. The path, query string, and page content are not inspected. A URL containing a username or password is rejected. If your original question concerns a particular server behind a domain, query that server's known public IP address directly instead of assuming that the domain identifies just one machine.
From a Domain to Its Network
A domain lookup requests both IPv4 and IPv6 address records. The summary distinguishes an empty answer for one family from a failure to retrieve that family. If IPv4 results are available but the IPv6 request fails, the page can still show the available results and explain the incomplete part.
Several addresses can be associated with one hostname. Each address section identifies the IP version, the routing origin information available for that address, and the source of that information. The set of returned addresses is a DNS result for this lookup; it is not a permanent inventory of every server serving the domain.
The tool limits how many addresses and detailed ASN records are processed in a single request. When a limit is reached, the page says that the result is truncated and identifies the available counts. That is a partial result, not a claim that the remaining addresses or ASNs do not exist. Individual addresses can be queried separately when they need further investigation.
Routing Origin and Registration
An origin ASN identifies the autonomous system reported as originating a route for the address. The matching route prefix shows the address block associated with that announcement in the selected routing source. This is routing information, not a statement that every address in the prefix is currently responding to connections.
The origin network and the organization holding an IP allocation can differ. For that reason, the address section includes a separate IP Registration Details action. Follow it when you need the registry information for the address block rather than the autonomous system that appears in routing data.
More than one origin can be returned for an address. The result lists the origins reported by the routing source. Do not infer a routing fault from the count alone. Understanding why multiple origins appear requires the relevant routing context, which this lookup does not establish.
A routing source can return no announcement for a valid public IP address. That means no matching route was available from that source for the lookup; it does not prove the address has never been used or is unreachable from every network. A source retrieval failure is shown separately so that missing evidence is not confused with an empty result.
Reading an AS Registration
The registration summary can include the record name, registered organization, regional registry, handle, country code, record type, status, and registration dates. Fields appear only when the registry supplies them; a missing field means that detail is unavailable in the returned record.
Some AS numbers are reserved for special uses rather than allocation to an ordinary public network operator. Those numbers receive a classification explanation. A valid numeric input can therefore produce a special-purpose result instead of a public organization record.
Where a returned registration covers a range of AS numbers, that range is shown alongside the queried number. It describes the registry object, not a list of every network the organization operates. The country code also belongs to the registration and should not be treated as a physical location measurement for a server or visitor.
Checking Sources and Timing
Routing information and registry information can come from different sources and can be retrieved at different times. The source and time fields preserve that distinction. Registration and last-changed dates refer to the record itself; a lookup timestamp does not replace those dates.
If a source is unavailable and a usable earlier result exists, the relevant section is marked as previously retrieved information. A warning can apply to only part of a combined domain lookup. Check the timestamp and freshness label in each address and registration section.
Copy Details collects the displayed query, address, registration, source, and time information. Keeping that context is useful when comparing a later lookup or discussing a network issue. Use New Lookup to replace the input. The page does not trace packet hops, list every advertised route, establish route authorization, or measure service availability.
When Only Part of a Lookup Succeeds
An address can have a reported routing origin even when the corresponding registration service is temporarily unavailable. You can still see the ASN match, but the lookup cannot confirm the registered organization from that response.
The reverse situation is also possible: a direct AS number lookup can return a registration even when an IP address lookup cannot retrieve routing data. A successful registration lookup does not prove that a particular prefix is currently announced by that ASN.
