# ASN Lookup

Look up an Autonomous System (AS) number through RDAP, from the Regional Internet Registry that allocated it (ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC). Accepts AS13335, as13335, 13335 or asdot such as 1.10. Returns the AS name and handle, the number range it belongs to, type, country, status, registration and last-changed dates, contacts and the abuse mailbox. Private-use, documentation and reserved AS numbers return status "special_purpose" without any lookup. This is registration data; it does not list prefixes, peers or routes.

**Not for:** Routing data such as announced prefixes, peers or BGP paths, IP addresses (use ip_whois) or domain names (use whois_lookup).

- Tool id: `asn-lookup`
- Category: ip
- Execution: network
- MCP tool `asn_lookup` at https://lookupowl.com/mcp
- REST `GET https://lookupowl.com/api/v1/tools/asn-lookup` (or POST a JSON body)
- OpenAPI: https://lookupowl.com/api/openapi.json

## Input

| Field | Type | Required | Default | Description |
|---|---|---|---|---|
| `q` | string | yes |  | AS number, e.g. AS13335, 13335 or asdot notation such as 1.10. A leading "AS" is optional. min length 1, max length 512 |
| `includeRaw` | boolean | no | `false` | Include the raw RDAP JSON from the Regional Internet Registry in the result. Large; off by default. |

## Output

Results are wrapped in an envelope: `tool`, `version`, `requestId`, `data`, `summary`, `meta` (cache status, timing), `permalink`. `data` has these fields:

| Field | Type | Description |
|---|---|---|
| `query` | object |  |
| `status` | "found" \| "not_found" \| "special_purpose" \| "no_rdap_service" | found: a record exists. not_found: the registry says there is none. special_purpose: reserved address space or AS number, nothing to look up. no_rdap_service: no RDAP (and for domains no WHOIS) service exists. |
| `source` | "rdap" \| "whois" \| "none" | Where the record came from. |
| `availability` | object | Domains only. "likely-available" is a registry saying there is no record; premium or reserved names can still be unavailable. |
| `registrar` | object | Outcome of asking the registrar after the registry. The merged data is in domain. |
| `whois` | object | Raw WHOIS reply, only when the TLD has no RDAP service. |
| `error` | object |  |
| `provenance` | object | How the answer was obtained: which bootstrap entry, which servers, timings. |
| `raw` | object | Raw upstream RDAP JSON. Only with includeRaw. |
| `autnum` | object |  |

## Examples

### AS13335 (Cloudflare)

```json
{"q":"AS13335","includeRaw":false}
```

```bash
curl 'https://lookupowl.com/api/v1/tools/asn-lookup?includeRaw=false&q=AS13335'
```

Web page: https://lookupowl.com/asn-lookup?q=AS13335

### AS15169 (Google), without the prefix

```json
{"q":"15169","includeRaw":false}
```

```bash
curl 'https://lookupowl.com/api/v1/tools/asn-lookup?includeRaw=false&q=AS15169'
```

Web page: https://lookupowl.com/asn-lookup?q=AS15169

### A private-use AS number has no owner to look up

```json
{"q":"AS64512","includeRaw":false}
```

```bash
curl 'https://lookupowl.com/api/v1/tools/asn-lookup?includeRaw=false&q=AS64512'
```

Web page: https://lookupowl.com/asn-lookup?q=AS64512

## Web pages

- https://lookupowl.com/asn-lookup

## Limits and caching

- Cost: 1 unit for a live lookup, 1 unit for a cached one. Budgets are per network and published in the `RateLimit` response headers.
- Cache: the lifetime follows the data (for DNS, the record TTL, within a few minutes). Add `fresh=true` (MCP argument or query parameter) to look again; it costs 3 units per unit and is limited to 10 per hour.
- Timeout: 15 s.

## Related tools

- [IP WHOIS Lookup](https://lookupowl.com/tools/ip-whois.md): Who owns an IPv4 or IPv6 address: network range, name, country, registry, abuse contact and origin AS, from RDAP.
- [IP Location Lookup](https://lookupowl.com/tools/ip-location.md): Where an IP address is: city, region, country and the network that runs it, from DB-IP, with an honest accuracy note.
- [Reverse DNS Lookup](https://lookupowl.com/tools/reverse-dns.md): Find the host name (PTR record) of an IPv4 or IPv6 address and check that it resolves back to the same address.
- [WHOIS Lookup](https://lookupowl.com/tools/whois-lookup.md): Registrar, creation and expiry dates, status codes, nameservers and DNSSEC for any domain, from RDAP with WHOIS fallback.
- [IP Subnet Calculator](https://lookupowl.com/tools/subnet-calculator.md): Network, broadcast, usable range, masks and exact host counts for any IPv4 or IPv6 subnet.

## Guide: ASN lookup

The network behind an AS number: who runs it, where it's registered and how to reach its abuse desk.

### What an ASN is and what you get

An autonomous system (AS) is a network, or a group of networks, run by one organisation under a single routing policy. Its AS number, or ASN, is the ID it uses to announce its IP address blocks to the rest of the internet over BGP, the protocol networks use to tell each other which addresses they can reach. Google uses AS15169, Cloudflare AS13335 and Amazon AS16509, and thousands of ISPs, universities and companies have their own.

This lookup returns the registration record for a number: who holds it, the name they gave it, the country, which of the five regional internet registries (RIRs) handed it out, when it was registered and last changed, and the abuse contact when one is published. It is the paper record. It does not say which address blocks the network announces today.

### How to use it

1. **Enter the number**: Accepted forms are `AS13335`, `as 13335`, `ASN13335` and plain `13335`. Asdot, the `high.low` form some routers and logs use, works too: `6.6784` is 6 * 65536 + 6784, which is AS400000.
2. **Read the holder and the abuse contact**: The holder is the organisation the registry holds responsible for the AS. The abuse contact is the right place to report attacks that come from its networks. Not every record publishes one, and the result says so when it does not.
3. **Start from an IP address instead**: Run the address through the [IP WHOIS lookup](https://lookupowl.com/ip-whois-lookup) to see who it is registered to. When the registry names an origin AS there, it links back to this page.

> **In Claude, ChatGPT or Cursor** Connect the LookupOwl MCP server and ask: “Who runs AS13335, and where do I report abuse?” The assistant calls `asn_lookup` and gets the AS name, the holder, the registry, the registration dates and the abuse contact. It returns the registration record only, with no prefixes or peers.

### Reading the result

- **Holder.** The organisation the registry says is responsible. It can be a parent company or a hosting provider rather than the brand you know.
- **Name.** A short label on the record, such as `GOOGLE` or `CLOUDFLARENET`. Some registries put an ID there instead, like `ORG-SL75-AFRINIC`. The registry's own ID for the record, the handle, is in the JSON.
- **Country.** The country on the record, or the one in the holder's postal address if the record has none. It says where the holder is based, not where its routers are.
- **Registry.** Which of ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC manages the number. A few records are answered by a national registry, such as Brazil's registro.br, and the Registry field reads Unknown for those.
- **Dates.** When the registry recorded the number and when it last changed.
- **A block, not one number.** Some numbers sit inside a range the registry gave to one organisation. AS8075 is part of AS8068 to AS8075, which belongs to Microsoft, and the result names that block.

Some numbers are reserved and have no public holder. LookupOwl explains them instead of failing, and asks no registry about them:

| ASN range | Meaning | Defined in |
|---|---|---|
| 0 | Reserved. Not a real network; used to say an address block must not be routed | RFC 7607 |
| 23456 | AS_TRANS: a stand-in for 32-bit ASNs in old software | RFC 6793 |
| 64496 to 64511 and 65536 to 65551 | Documentation and examples | RFC 5398 |
| 64512 to 65534 and 4200000000 to 4294967294 | Private use | RFC 6996 |
| 65535 and 4294967295 | Reserved | RFC 7300 |
| 65552 to 131071 | Reserved by IANA, not yet assigned | IANA AS numbers registry |

### Common problems

- **Not allocated.** A number that IANA has not yet handed to any registry, such as AS250000, is reported as not allocated.
- **No record.** The number falls in a registry's range, but the registry has no record of it. Check for a typo first.
- **Private or reserved number.** Private numbers turn up inside company networks and with providers that strip them from routes. They have no public record. The table above lists them.
- **The holder is not the website owner.** Networks are often run by a subsidiary, a hosting company or a managed-service provider.
- **The registry did not answer.** You will see a retry message, or a recent stored copy that is labelled as one. Wait a minute and try again.

### How the lookup works

The number is turned into a plain integer and checked against the reserved list above first, so special numbers are answered without any request. For the rest, LookupOwl finds the registry in IANA's AS number bootstrap file and asks that registry's RDAP server (RDAP is the modern, JSON replacement for WHOIS) for `/autnum/<number>`. It follows any redirect, for example from LACNIC to a national registry, and shows the `autnum` object that comes back. Recent answers are kept briefly so repeat lookups are quick.

```bash
# Same data from a terminal
curl -sL https://rdap.org/autnum/13335 | jq '{handle, name, startAutnum, endAutnum}'

# Classic WHOIS
whois AS13335
```

### Standards

- **RFC 4271**: BGP-4, where AS numbers are used for routing.
- **RFC 6793**: 4-byte AS numbers. **RFC 5396**: the asplain, asdot and asdot+ ways of writing them.
- **RFC 5398, RFC 6996, RFC 7300, RFC 7607**: documentation, private and reserved AS numbers.
- **RFC 9082, RFC 9083 and RFC 9224**: the RDAP `/autnum/` query, the `autnum` object it returns and the IANA bootstrap file that says which registry to ask.

### Frequently asked questions

**What does ASN stand for?**

ASN stands for autonomous system number. It names a whole network, so it is not an IP address and does not point at one machine. One ASN usually covers many address blocks. IANA gives each registry ranges of numbers, and the registry hands them to the organisations it serves.

**How do I find the ASN of an IP address?**

Ask a BGP service, because the AS that announces an address is routing data, not registration data. Sites such as bgp.tools, bgp.he.net and RIPEstat show it. The [IP WHOIS lookup](https://lookupowl.com/ip-whois-lookup) here lists origin AS numbers only when the registry publishes them, which few do, so a missing one is normal. Once you have the number, paste it above to see who holds it.

**Can an organisation have more than one ASN?**

Yes. Large companies often run several, for example one per region or one inherited from an acquired business, and some networks use separate ASNs for transit and for customers. Each number has its own record, so look each one up to see which holder and abuse contact it points to.

**Who should I contact about abuse from an AS?**

Use the abuse contact on the AS record. If the trouble comes from one address, the abuse contact on that address's network, which the [IP WHOIS lookup](https://lookupowl.com/ip-whois-lookup) shows, is usually the better target. Send the date, the time zone and a few log lines, and skip large attachments. Some records publish no abuse contact, and the result says so.

**What is a 4-byte ASN?**

A 4-byte ASN is a 32-bit AS number. The original 16-bit numbers stopped at 65535 and began to run short, so RFC 6793 extended the range to 4,294,967,295. Numbers above 65535 are sometimes written in asdot as two parts, high then low, so `2.0` is AS131072. This tool accepts both spellings.

**Do you show prefixes, peers and RPKI status?**

No, this page shows the registry record only. Prefixes (the address blocks a network announces), upstream providers, peers and RPKI status (whether the address holder has approved an announcement) change often and come from BGP route collectors. For those, use a looking glass (a public view into a router's routing table) or a service such as bgp.he.net, bgp.tools or RIPEstat.

**Can I look up an ASN from a script or an AI assistant?**

Yes. The `asn_lookup` tool is on the free REST API and the MCP server, with no key. It returns the same record as structured data, and the raw RDAP JSON if you ask for it, but no prefixes or peers. See [LookupOwl with AI agents](https://lookupowl.com/learn/lookupowl-mcp-ai-agents).