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Run a reverse NS lookup by entering any name server hostname to discover every domain that delegates its DNS to it. Map provider footprints, audit migrations, and group domains by who runs their DNS.
DNS itself has no way to answer this question. Delegation is recorded in the parent zone and points downward, from zone to name server, and a name server will not enumerate the zones it hosts. Reverse NS lookups are made possible by large passive DNS datasets that index NS records across the internet, then let you query that index in reverse.
When you run a search, the tool queries an indexed database of DNS records collected from domains across the global DNS. It matches your input against the value of every stored NS record and returns the domains that delegate to it.
How the input is matched depends on whether you use a wildcard:
| Input | Matching | What It Matches |
|---|---|---|
| ns1.cloudns.net | Exact hostname | Only domains delegated to the exact host ns1.cloudns.net |
| n*.cloudns.net | Wildcard | Domains delegated to any cloudns.net name server starting with n, such as ns1, ns2, and ns3 |
| *.awsdns-01.com | Wildcard | Domains delegated to any name server under awsdns-01.com |
Input is validated before the request is sent, so anything that is not a well-formed name server hostname or wildcard pattern is rejected in the form with a clear message. Because managed DNS platforms serve very large numbers of zones, wildcard searches against a big provider can take noticeably longer than an exact hostname and are returned one page at a time.
| DNS Lookup | Reverse NS Lookup | |
|---|---|---|
| Input | A domain name (example.com) | A name server hostname (ns1.cloudns.net) |
| Output | The NS records that domain delegates to | All domains delegated to that name server |
| Data source | Live DNS query against authoritative name servers | Indexed passive DNS database |
| Primary use | Verifying which name servers a domain uses | Provider footprint mapping, migration audits, and DNS investigations |
A provider's name servers are the clearest signal of which domains sit on its platform. Searching a name server pool shows the scale of that footprint, which is useful for competitive research, market sizing, and understanding how much of a portfolio depends on a single DNS vendor.
After moving zones to a new DNS provider, a reverse NS lookup on the old name servers shows which of your domains are still delegated there. It is a fast way to catch domains that were missed during a cutover, before stale records or an expiring account take them offline.
An NS record names an authoritative server for a zone. The delegation lives in the parent zone, which is why a registrar change propagates from the TLD downward, and most domains list two or more name servers for redundancy. Each record carries a TTL that tells resolvers how long to cache the delegation. A single name server can be authoritative for millions of zones, which is exactly the relationship a reverse NS lookup uncovers.