Find Company IP Ranges and ASN: A Registry Walkthrough

To find a company’s IP ranges, search its name in the regional internet registries, look for an autonomous system number (ASN) and list the prefixes that ASN announces. Many businesses have no ranges of their own, and a registered block does not prove who is browsing from it.

The three layers of data

Layer	What it tells you	Where to look
Allocation and assignment	Which organisation holds a block	Regional registries (ARIN, RIPE NCC and others)
Routing	Which ASN announces the block on the internet	Public routing data and looking-glass tools
Naming	Hints in reverse DNS	dig -x or host on an address

An IP to company service joins these and adds classification. If you want to understand what such a service is doing, or sanity-check an answer, you can walk through the same layers by hand. The overall concept is covered in how IP to company lookup works.

Step-by-step: from a company name to ranges

1. Search the registry by organisation name. The RIPE Database and ARIN’s whois both support organisation searches. Start there for companies in Europe and North America respectively; other regions have their own registries.
2. Note the organisation handle and any related records, since large firms often have several.
3. Find ASNs linked to the organisation. If the record lists an aut-num or ASN, write it down.
4. List announced prefixes for that ASN using a public routing-data tool.
5. Check reverse DNS for a few addresses in each prefix. Hostnames such as office or vpn labels hint at use.
6. Classify. Is the holder a company, an ISP, a cloud host or a security vendor? That determines whether the block can tell you anything about visitors.

Step-by-step: from an address to an owner

Going the other way is what visitor analysis needs.

1. Query the address in a whois tool; the query will redirect to the right registry.
2. Read the organisation and the network name.
3. Look up the ASN announcing the prefix.
4. Compare: if the holder and the ASN operator are an ISP or hosting company, stop. The address is shared.
5. If the holder is a company that runs its own network, you have a strong clue.

The free reverse IP lookup tool from BusinessMCP does steps 1 to 5 in one click and shows a company name and domain for corporate networks, or a provider label otherwise. See reverse IP lookup for company names for a guided version.

Key takeaway: registry data tells you who holds an address block. It does not tell you who is using an address right now. That gap is the whole reason classification exists.

Why registered does not mean used

Several things break the link between holder and user.

• Leasing. Companies and ISPs lease address space to others, and registry records may lag.
• Hosting. A company’s block may hold public servers, not employee desktops.
• Customer assignment. ISPs assign blocks to business customers; some are recorded, many are not.
• Cloud. Cloud providers hold huge blocks used by thousands of unrelated customers.
• Transfers. Addresses change hands and registry updates take time.

A service that rebuilds its data regularly narrows this gap. BusinessMCP’s page says its graph rebuilds nightly from public registry, routing and DNS data plus confirmations from its own product, and that a range that changed hands today can be a day behind. That timing detail is worth asking any vendor.

What the records often look like

Record field	Example meaning	Caution
Organisation	Legal name of the holder	May be a parent company
Network name	Short label	Not always meaningful
Country	Registration country	Not necessarily where users are
ASN	Operator number	Shared by many customers on ISP or cloud ASNs
Abuse contact	Who handles complaints	Usually not the end user

Always record the date you looked, since all of these change.

Using ranges practically

If you do find a customer’s or target account’s ranges, you can:

• Exclude them from your own analytics, if they are yours or your partners’.
• Cross-check a vendor’s answer on a handful of addresses.
• Build an allowlist of known account networks to boost in scoring; see lead scoring with IP data.

You should not:

• Treat every address in a range as one person.
• Assume ranges are exclusive; carve-outs exist.
• Store the information beyond what you need; see GDPR and IP lookup.

When to stop doing this by hand

Manual research is a fine way to learn and to settle disputes about a single address. For a day of logs it is not workable. Use an API such as BusinessMCP’s IP to company API, the bulk route or another service you have tested using the evaluation method.

Checklist

• Find the registry for the address or organisation.
• Record holder, network name and ASN with the date.
• Check who operates the ASN.
• Classify holder: company, ISP, cloud, security vendor.
• Remember that holder is not the same as user.

Reading an ASN entry

When you find an ASN, the information worth recording is short. Note the operator name, the country, the number of prefixes announced and the upstream providers, if your routing tool shows them. A network with a handful of prefixes and one upstream is usually a single organisation. A network with thousands of prefixes announced to many peers is usually an ISP, a cloud or a content network, where one ASN covers a vast number of unrelated end users. That ratio of prefixes to upstreams is a quick, rough guide to whether an ASN is worth treating as a single customer.

Mistakes to avoid

• Treating an ISP’s ASN as the visitor. The ASN of a broadband provider tells you nothing about the household.
• Copying ranges into allowlists without a review date. Blocks are reassigned; schedule a refresh.
• Using geolocation as ownership. Where an address appears to be is not who runs it.
• Mixing up the parent company and the subsidiary. Registry names often show the legal entity, which may differ from the brand in your CRM; match on domain where you can.
• Searching only one registry. A global organisation may hold blocks in several regions, so repeat the search across registries.

For automation of this entire chain, with classification added, see how a service documents its approach in BusinessMCP’s IP API overview, and compare it with at least one alternative using our selection guide.