A reverse IP lookup takes an IP address and tells you which hostname, domain or network it belongs to. It is the opposite of a normal DNS lookup, which starts with a domain like example.com and returns its IP address.
For B2B marketing and sales, the useful version goes one step further. Instead of a hostname, you want the company behind an IP address, so you can see which businesses visit your website even when they never fill in a form. This guide covers both: how to run a reverse IP lookup yourself, and how IP-to-company data works.
What is a reverse IP lookup?
The Domain Name System (DNS) is the internet’s address book. When you type a domain into your browser, DNS translates it into the IP address of the server that hosts it. That is a forward lookup.
A reverse lookup runs the same question backwards. You start with an IP address and ask what name is attached to it. In practice, “reverse IP lookup” is used for three different things:
- Reverse DNS (rDNS). Returns the hostname stored in the IP’s PTR record, for example 8.8.8.8 resolves to dns.google. Network owners set these records themselves, so many IPs have a generic hostname or none at all.
- Reverse IP domain lookup. Lists the websites hosted on the same IP address. This is useful on shared hosting, where hundreds of domains can sit on one server.
- IP to company lookup. Tells you which organisation is using an IP address. This is what B2B teams need to identify the companies visiting their website.
Reverse IP lookup vs. IP to company lookup
| Reverse DNS / reverse IP | IP to company | |
|---|---|---|
| Input | An IP address | An IP address |
| Output | A hostname or a list of domains | A company name, domain, industry, size and location |
| Data source | Public DNS records | DNS, network registration data and other signals, combined and maintained by a data provider |
| Typical user | IT, security and SEO teams | Marketing, sales and RevOps teams |
| Answers | “Which server or website is this?” | “Which business is on our website?” |
How to do a reverse IP lookup
You can run a reverse DNS lookup from any computer without installing anything.
On Windows
Open Command Prompt and type nslookup followed by the IP address, for example nslookup 8.8.8.8. The “Name” line in the answer is the hostname.
On macOS and Linux
Open Terminal and use dig -x 1.1.1.1 or host 1.1.1.1. Both return the PTR record, in this case one.one.one.one.
With an online tool
Free reverse IP tools let you paste an IP address and see its hostname, and often the other domains hosted on the same server. They are quick for one-off checks, but they do not tell you which company a visitor works for.
Check who owns the network
If the hostname tells you nothing, look up the IP in a regional internet registry such as RIPE, ARIN or APNIC (a WHOIS or RDAP lookup). It shows which organisation the IP range is registered to. For an office network that can be the company itself. For most home and mobile connections it is the internet provider.
How to find the IP address of a website
If you need the opposite, a website’s IP address, run a forward lookup:
- Windows:
nslookup example.com - macOS and Linux:
dig +short example.comorhost example.com - Any system:
ping example.comshows the IP it connects to.
Large sites often return several IP addresses, or the address of a CDN such as Cloudflare rather than their own server. That is normal: the CDN sits in front of the site and answers on its behalf.
How to identify the company behind a website visitor
Every visit to your website comes from an IP address. A reverse DNS lookup on that IP rarely gives you a company name, because:
- Most people browse through an internet provider, so the hostname belongs to the provider, not the employer.
- Many companies route traffic through cloud security services or VPNs.
- Remote and hybrid workers often connect from home networks.
IP-to-company providers solve this by building a database that maps IP ranges to the organisations using them. They combine registration data, DNS records and other signals, and keep updating the map as networks change. When a visitor lands on your site, the IP is matched against that database and you see the company, not the person.
No provider can identify every visitor. Home connections and mobile networks usually cannot be tied to a company, so expect a share of your B2B traffic to be identified, not all of it. Test any tool on your own traffic before you buy. For every method, from forms to intent data, see our guide on how to identify website visitors.
Is reverse IP lookup GDPR compliant?
Looking up public DNS records is not a privacy issue. Identifying website visitors is different, because IP addresses can count as personal data under GDPR. A B2B tool should therefore identify companies rather than individuals, have a documented legal basis such as legitimate interest, and offer a data processing agreement.
Albacross is built in Stockholm for GDPR and CCPA. Our data processing agreement is public.
How B2B teams use IP-to-company data
Knowing which companies visit is only useful if someone acts on it. The teams that get the most out of it follow the same steps:
- Identify the companies. Add a tracking script to your site and see which businesses visit, which pages they read and how often they return. See how Albacross identifies website visitors.
- Prioritise by intent. A company that reads your pricing page three times this week matters more than one that read a blog post once. Albacross scores each account on its visits, its fit and the topics it researches elsewhere on the web, using Bombora data.
- Route it to the right person. Send high-intent accounts to your CRM, Slack or Teams so sales can follow up the same day. See how Automate works.
- Reach the buying group. Find decision makers at the account and contact them, or show them ads. See Engage.
If you are building a product and need IP-to-company data inside it, the Albacross IP to Company API resolves an IPv4 address to company name, domain, size, revenue, industry and location in one call.
Want to see which companies are on your website right now? Try Albacross free for 14 days.
Frequently asked questions
Can a reverse IP lookup identify a person?
No. A reverse IP lookup returns a hostname, domain or the organisation that uses the network. It does not reveal names, email addresses or other personal details of the visitor.
Why does a reverse IP lookup show my internet provider?
Because the provider owns the IP address and sets its reverse DNS record. Unless a company runs its own network with its own records, the lookup will show the provider.
How accurate is IP to company data?
It depends on the provider and on your traffic. Office and corporate network traffic matches well. Home, mobile and VPN traffic often cannot be matched. Run a trial on your own site to see the real rate.
Is there a free reverse IP lookup?
Yes. The nslookup, dig and host commands are free and built into every operating system, and many websites offer free reverse IP tools. For company-level data on your website visitors you need an IP-to-company provider such as Albacross.
What is the difference between reverse DNS and reverse IP?
Reverse DNS returns the single hostname set in an IP’s PTR record. A reverse IP domain lookup lists every website hosted on that IP. People often use the two terms for the same thing.
Further reading
Marcus Svensson
Head of Growth
Overview only the features needed for your use case- Show how to adapt it to your customer qualification process
