ASN Lookup

Start with the public IP address and run it through an IP-to-ASN lookup. The useful result is not only the AS number, such as AS15169, but also the AS name, routed prefix, country, and the Regional Internet Registry record behind it. The routed prefix tells you which block is being announced, for example 8.8.8.0/24 instead of only 8.8.8.8. A useful habit is to cross-check the ASN with WHOIS or RDAP when ownership matters, because routing data and registration data can describe different parts of the same story.

Paste the IP address into the lookup and read the AS number, AS name, and country fields together. The AS number identifies the network that is currently originating or announcing the route for that IP on the internet. For example, a result may show an address belongs to a cloud provider ASN, even when the final customer is using the service. That is normal. Treat the ASN as the routing owner or operator view, then use the registered organization and RIR details when you need administrative ownership or abuse-contact information.

To look up the owner of an AS number, search the ASN itself, such as AS64512 or 64512, and read the registry organization, handle, country, and contact fields. ASNs are allocated through Regional Internet Registries, so the data usually comes from ARIN, RIPE NCC, APNIC, LACNIC, or AFRINIC. Separate two ideas: the registered ASN holder and the network currently using it in BGP. They are often the same, but acquisitions, customer routing, or managed services can make the lookup require a second check.

Finding all IP ranges for an ASN means looking at the prefixes that ASN announces in BGP, not just every address ever registered to the organization. Enter the ASN and review the visible prefixes, such as 203.0.113.0/24 or 2001:db8:100::/48. Announced prefixes can change as traffic engineering and provider relationships change. Registered ranges may include space that is not currently routed, while BGP output shows what the internet can see right now. For firewall work, use announced prefixes carefully and verify them before applying rules.

An ASN and an IP address are related, but they are not the same thing. An IP address identifies a host or a network location, such as 192.0.2.10. An ASN identifies a network operator or routing domain that exchanges routes with other networks. Think of the IP address as the street address and the ASN as the transport company controlling a group of routes. A single ASN can announce many prefixes, and one organization can own several ASNs. This distinction becomes important when troubleshooting routing, filtering, and ownership questions.

To check BGP prefixes for an ASN, enter the AS number and look at the list of prefixes visible from public route collectors. Each prefix should show the origin ASN and sometimes an AS path. A prefix like 198.51.100.0/24 being originated by one ASN means that ASN is advertising reachability for that block. Compare results from more than one collector when the issue is serious, because BGP visibility depends on where the observer is connected. Propagation, filters, and RPKI validation can all affect what you see.

The RIR registry for an ASN depends on where the number resource was allocated. A good lookup will usually show whether the record belongs to ARIN, RIPE NCC, APNIC, LACNIC, or AFRINIC. Once you know the registry, check the ASN object for organization name, status, country, and contact details. This is useful when someone asks, 'Who should I contact?' The registry record is the administrative source, while BGP tables show routing behavior. Use both views when you need confidence before reporting abuse or planning peering work.