Reverse IP lookup resolves a public IP address to the organization that owns or leases it. Free tools include ipinfo.io, ARIN WHOIS, and BGPView — accuracy ranges from 40-80% depending on whether the IP is corporate (allocated) or consumer (dynamic ISP).
Reverse IP lookup is the foundation of B2B visitor identification. Given a public IP, resolve it to the organization that owns or leases it. Here's how it works, what's free, and where the accuracy ceiling is.
## The Three Data Sources 1. **WHOIS** — public IP block allocation records maintained by ARIN/RIPE/APNIC/AFRINIC/LACNIC. Returns the org that leases the range. 2. **ASN + BGP** — Autonomous System Numbers group thousands of IPs under one routed operator. Reveals whether an IP belongs to a corporate ASN (Acme's own AS) or an ISP AS (Comcast). 3. **Reverse DNS (PTR)** — often the operator sets a descriptive PTR record: `mail-01.acme.com` → Acme.
## Free Tools You Should Bookmark - [ipinfo.io](https://ipinfo.io) — org, ASN, geo. Free 50k lookups/month. - [BGPView](https://bgpview.io) — ASN + BGP peer + IP block owner. - [Hurricane Electric BGP](https://bgp.he.net) — deep BGP inspection. - [ARIN WHOIS](https://whois.arin.net) — North American allocations. - [RIPE Database](https://apps.db.ripe.net) — European allocations.
## Corporate vs Consumer IPs The biggest determinant of accuracy is whether the IP is corporate or consumer: - **Corporate** — statically assigned, leased directly by the company or via their ISP. Resolves cleanly. - **ISP dynamic pool** — rotates between residential customers. Resolves to the ISP. - **Mobile** — worst case. Carrier-grade NAT means thousands of users share one IP. Resolves to the carrier. - **VPN / Proxy / Cloud** — resolves to the VPN/cloud provider, not the actual user.
## When Reverse IP Lookup Fails - The IP is in a VPN range → you get 'NordVPN' not the real company - The IP is a cloud NAT gateway → you get 'AWS' not the tenant - The IP is on a shared consumer ISP pool → you get the ISP - The company routes egress through a residential proxy → useless Expect a 30-50% resolution rate on total traffic, higher on business-hour desktop.
## Using It for B2B Visitor Identification One-off reverse lookups are fine for research. For **live visitor identification** you need: - A first-party pixel that captures the IP + browser fingerprint - A live business-IP dataset with 5+ million corporate ranges - ISP/VPN/proxy filtering (rejects consumer IPs from the feed) - Firmographic enrichment (industry, size, tech stack) Building this pipeline in-house is a multi-quarter project. See [How LemReveal Identification Works](/help/how-identification-works) for the productised version.
The core tools are free. ipinfo.io, ARIN WHOIS, BGPView, and reverse DNS are all free and require no login for reasonable use. Paid services (IPinfo, MaxMind GeoIP2) add higher rate limits and richer B2B firmographics.
On corporate/static IPs, 70-90% resolve to the correct company. On consumer/mobile IPs, accuracy drops to 10-20% because dynamic ISP pools don't map to a single org. Business-hour desktop traffic gives the best accuracy.
Yes — via IPinfo API, MaxMind GeoIP2, or by ingesting BGP + WHOIS dumps directly. LemReveal's pixel does this in real-time for every visitor, so you don't need to build the pipeline yourself.
Residential/mobile ISPs (Comcast, Sky, Free, Deutsche Telekom, Vodafone) issue dynamic IPs from a shared pool. Even if someone from Acme Corp is browsing from home, their IP resolves to the ISP, not Acme. Business-hour traffic from a corporate network is the sweet spot.
Geolocation returns city/region — useful for localization. Reverse lookup returns the owning organization — useful for B2B identification. Most tools do both.
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