IP Tools
Reverse IP Lookup: Domains Hosted on an IP Address
A reverse IP lookup finds the domains currently or historically hosted on a given IP address. It is useful for security research (identifying co-hosted suspicious sites), SEO due diligence (avoiding bad neighborhoods on shared hosting), and investigation work (mapping infrastructure relationships).
What It Measures
This tool measures co-hosted domains by querying public DNS and passive DNS databases for any hostname that resolves to the supplied IP. It returns the list of domains, with timestamps where available, plus the IP's PTR record (reverse DNS).
How It Works
- Accepts any valid IPv4 or IPv6 address
- Queries reverse DNS (PTR) for the canonical hostname
- Searches passive DNS sources for any A or AAAA records pointing at the IP
- Returns the deduplicated list of domains with first and last seen dates
Why It Matters
Shared hosting providers often host hundreds of unrelated sites on a single IP. If one of those sites engages in spam or malware, the IP can get blacklisted, hurting deliverability or rankings for your site. Reverse IP lookup tells you who you are sharing an IP with so you can decide whether to move.
Understanding Your Results
A dedicated IP returns just your own domains. A shared hosting IP returns dozens to thousands. The lookup works best on stable IPs with long term DNS history. CDN edge IPs (Cloudflare, Fastly) intentionally serve many domains and reverse lookup results there are usually only a small sample.
Frequently Asked Questions
Why would I do a reverse IP lookup?
Common reasons include checking if a shared hosting IP has bad neighbors that could affect SEO or email deliverability, mapping out an organization's infrastructure for security research, verifying that a hostname resolves to the IP you expect, and investigating whether multiple suspicious domains share the same hosting infrastructure.
Is a reverse IP lookup the same as reverse DNS?
No. Reverse DNS (PTR record) returns one canonical hostname for an IP, set by the IP owner. Reverse IP lookup returns all domains hosted on that IP, derived from forward DNS history. The PTR record is one piece of data; the reverse IP lookup is a much broader search across DNS history.
Can I find every site on a CDN IP?
Generally no. Cloudflare, Fastly, and other CDN edge IPs serve millions of sites that resolve to the same IP. Reverse IP lookup tools only see the small subset of those domains that have been observed in passive DNS or other public sources. The full list is not typically discoverable from outside the CDN.
Is reverse IP lookup legal?
Yes. Reverse IP lookup uses only public DNS data and observed records, not anything private. It is widely used by security researchers, SEO professionals, and IT investigators. It does not access any private information about the sites or their owners; it just maps which domains point to which IPs.
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