ASN WHOIS Lookup
Look up any autonomous system number to see who operates it, where it is registered, and which IP prefixes it announces to the global routing table.
About ASN WHOIS Lookup
An autonomous system (AS) is a network, or group of networks, run under a single routing policy - typically an ISP, cloud platform, hosting company, university or large enterprise. Each one carries a globally unique autonomous system number, the identity it uses in BGP to exchange routes with the rest of the internet. Enter a number such as AS8309 (with or without the AS prefix) and this tool returns the operating organisation, its country, the responsible regional internet registry and the address space the network currently routes.
The lookup runs server-side from our EU infrastructure and assembles its answer from three live sources in parallel. It walks the WHOIS referral chain starting at IANA over TCP port 43, following referrals to the registry that actually manages the number - RIPE NCC, ARIN, APNIC, LACNIC or AFRINIC - and returns the raw record from each hop. In parallel it queries RDAP for structured registry data and pulls the current list of announced prefixes from public BGP routing data.
The announced-prefix list is the network's real footprint in the global routing table: the IPv4 and IPv6 ranges the AS originates right now. That makes it useful for confirming which blocks a transit or hosting provider genuinely routes before you peer with or allow-list them, for mapping the reach of an operator, or for tracing the network behind an address you have seen in a log or traceroute. The WHOIS records also carry the abuse and technical contacts you need when reporting activity from a network.
An ASN lookup answers a different question from an IP WHOIS: this describes the whole network - its operator, registry and routed prefixes - whereas an IP WHOIS describes the registration of a single address or block. Reach for this tool when you start from an AS number, for example one surfaced by a BGP looking glass or an upstream provider.
How to use it
- 1Enter the AS number in the field - AS8309, as8309 and 8309 all resolve to the same network.
- 2Select Lookup ASN; the query runs on our EU servers against registry and routing data.
- 3Read the announced-prefixes panel for the IPv4 and IPv6 ranges the network currently originates in BGP.
- 4Scroll the WHOIS hops to find the owning organisation, country, registry and abuse contact.
Common use cases
- -Identify the operator and country behind an AS number seen in a traceroute, BGP looking glass or firewall log.
- -Confirm which IP prefixes a hosting or transit provider actually announces before peering or allow-listing.
- -Find the abuse or technical contact for a network when reporting spam, scanning or other activity.
- -Map the routed address-space footprint and registry of a provider for due diligence or network research.
Frequently asked questions
- What is an ASN (autonomous system number)?
- An ASN is a globally unique identifier for an autonomous system - a network or set of networks operated under one routing policy, such as an ISP, cloud or hosting provider. It is the identity networks use in BGP to exchange routes across the internet.
- How do I find the owner of an AS number?
- Enter the number into the ASN WHOIS Lookup. It returns the operating organisation, its country and the responsible regional internet registry - RIPE NCC, ARIN, APNIC, LACNIC or AFRINIC - drawn from the registry's WHOIS and RDAP records.
- What are announced prefixes?
- Announced prefixes are the IPv4 and IPv6 address ranges an autonomous system currently originates in the global BGP routing table. They show the address space the network is actually routing at the moment of the lookup.
- What is the difference between an ASN lookup and an IP WHOIS?
- An ASN lookup describes an entire network - its operator, registry and routed prefixes - while an IP WHOIS describes the registration of a single address or block. Use an ASN lookup when you begin with an AS number.
- Do I need to type AS before the number?
- No. The tool accepts the number with or without the AS prefix, so AS8309, as8309 and 8309 are all treated as the same autonomous system.
- Where does the ASN data come from?
- It is assembled live for each request from the IANA WHOIS referral chain to the responsible registry, RDAP registry data and current BGP routing data, rather than from a stale cached database.