ASN Lookup / Whois

ASN Lookup / Whois

Every block of IP addresses on the public internet is announced by a network operator via BGP, the routing protocol that glues the internet together — and each operator is identified by an Autonomous System Number (ASN), a short integer like 15169. Looking up which ASN announces a given IP address answers the practical question "who runs this network?" long before a full whois record does: an ASN maps to a single organization (an ISP, a cloud provider, a university, a company's own network), while a whois record for the IP block itself is often registered to whichever hosting or transit provider technically owns the address space.

This tool resolves the origin ASN for an IP address using Team Cymru's public IP-to-ASN DNS service — a live, authoritative BGP-derived mapping refreshed continuously from the global routing table, not a static snapshot. Alongside the ASN itself you get the AS holder's name, the specific prefix (CIDR block) that ASN announces containing your address, which regional internet registry (ARIN, RIPE, APNIC, LACNIC or AFRINIC) allocated it, and — when our offline database has a match — the registered organization name and domain. A short RDAP whois summary (network name, registration handle, and registrant country) rounds out the picture with the same baseline detail our main API's network group carries.

You can also look up an AS number directly — type "AS15169" or just "15169" — to get that ASN's holder name without starting from an IP address, useful when you already know the AS number from a traceroute, a BGP looking-glass, or a peering database and just want to confirm who it belongs to. A direct AS-number lookup only returns the holder name: without a source IP address there is no offline organization/domain match and no RDAP record to attach, since RDAP records are delegated per IP block, not per ASN.

You can also open the complete, aggregated prefix list for an AS number. The list is generated from our indexed IPv4 and IPv6 assignment data and is paginated for large networks. For domain names, use the public domain RDAP endpoint at /api/v1/domain/{domain}; it follows IANA RDAP delegation and returns the registry's structured domain record. This product uses RDAP over HTTP only and does not fall back to port-43 WHOIS.

How to use this lookup

1. Enter an IP or AS number

   Type an IPv4 or IPv6 address (like 8.8.8.8) to find who announces it, or an AS number (AS15169 or just 15169) to find that AS's holder name directly.

2. Look up

   Click "Look up" (or open a permalink URL) to query Team Cymru's live BGP-derived ASN mapping and our RDAP whois client.

3. Read the result

   For an IP address you get the origin ASN, AS holder name, announced prefix, registry, allocation date, organization/domain (when available) and an RDAP whois summary; for an AS number you get just the holder name.

4. Share

   The page URL updates with your query as a permalink, so you can copy and share the current result directly.

Glossary

ASN

Autonomous System Number — the number identifying a network operator's routing domain, used in BGP to determine which organization announces a given block of IP addresses.

Origin ASN

The ASN that first announces (originates) a given prefix into the global BGP routing table — the network operator actually responsible for that address block, as opposed to any transit provider carrying its traffic.

Whois

The general term for a public directory of who registered a resource — an IP block, an ASN, or a domain name — with a regional or domain registry. RDAP is the modern, structured protocol that replaced the old plain-text WHOIS protocol for IP and ASN records.

RDAP

Registration Data Access Protocol — a structured, JSON-based successor to WHOIS for looking up who a block of IP addresses (or an ASN) is registered to, including the network name, a registration handle, and registrant details.

RIR

Regional Internet Registry — one of five organizations (ARIN, RIPE NCC, APNIC, LACNIC, AFRINIC) that allocate IP address blocks and AS numbers within their region and run the authoritative RDAP/whois servers for them.

BGP

Border Gateway Protocol — the routing protocol autonomous systems use to announce which IP prefixes they originate and exchange reachability information, forming the internet's global routing table.

API equivalent

This page calls our own public tools endpoint under the hood — you can call the same endpoint directly, unauthenticated, subject to a per-caller rate limit. The endpoint returns the complete, aggregated and paginated prefix list for an ASN; our full API's network group also returns the same ASN/RDAP facts as part of a larger per-IP lookup, for integrating into your own tools:

curl "https://ip.xakki.pro/api/v1/tools/asn?q=8.8.8.8"

Example response:

{
  "query": "8.8.8.8",
  "queryType": "ip",
  "asn": "15169",
  "allAsns": ["15169"],
  "asName": "GOOGLE, US",
  "prefix": "8.8.8.0/24",
  "registry": "arin",
  "allocated": "1992-12-01",
  "org": "Google LLC",
  "domain": "google.com",
  "rdap": {"country": "US", "handle": "NET-8-8-8-0-1", "name": "LVLT-GOGL-8-8-8"}
}

Read the full API docs

Related tools

• All free tools
• IPv4 Subnet Calculator
• Bulk IP List Classifier
• IP Geolocation API

Frequently asked questions

What's the difference between an ASN lookup and a whois lookup?

An ASN lookup answers "which network operator announces this address in BGP" — a live routing fact. A whois (RDAP) lookup answers "who is this IP block registered to at the regional registry" — a registration fact, which can differ from the announcing operator (e.g. a hosting provider registers the block, a customer's own ASN announces part of it). This tool gives you both for an IP address.

Why does looking up an AS number directly give me less than looking up an IP?

Because a bare AS number has no address attached: the offline organization/domain match and the RDAP whois record are both keyed off a specific IP block, not an ASN, so neither applies without a source IP. Only the AS holder name — which Team Cymru's ASN.<n> DNS record carries directly — is available for a bare AS-number query.

How can I see every prefix an ASN announces?

Open the complete, aggregated and paginated prefix list for the AS number. It is generated from our indexed IPv4 and IPv6 assignment data.

Can I look up whois for a domain name instead of an IP or ASN?

Yes. Domain lookups are served by the public RDAP-only endpoint /api/v1/domain/{domain}, which follows IANA RDAP delegation and returns the registry's structured domain record. The ASN Lookup form itself accepts only an IP address or AS number; it does not use a port-43 WHOIS fallback.

Does this tool log or store the addresses I look up?

Your query is sent to our server to perform the live lookup (unlike our purely client-side calculators), but results are cached briefly to spare the upstream Team Cymru and RDAP services from repeated identical queries — the same short-lived cache our main API uses, not a permanent record tied to you.

Is there a rate limit on this tool?

Yes — this page and its underlying API endpoint share the free tools lane's per-caller rate limit, independent of our main IP lookup API's daily quota. If you need higher volume or programmatic access, our API docs cover the paid tiers.