Reverse DNS Lookup
Enter an IP address to find the hostname it points back to, if its owner has published one.
The hostname appears here, along with the exact name that was queried.
What reverse DNS is
Ordinary DNS turns a name into an address. Reverse DNS does the opposite: it asks which name an address claims as its own. The answer is stored in a PTR record.
To make this work with the same system, the address is rewritten as a special name. An IPv4 address is reversed and placed under in-addr.arpa, so 203.0.113.42 becomes 42.113.0.203.in-addr.arpa. An IPv6 address is expanded, reversed one digit at a time, and placed under ip6.arpa. The tool shows the name it queried so you can see this for yourself.
Who controls the answer
The owner of the address block sets the PTR record. That is usually the internet provider or hosting company, not whoever runs a website on the address. This is why a site's domain name and the reverse name for its address often do not match, and why many addresses have no reverse name at all.
What it is used for
- Email. Mail servers check that a sender's address has a reverse name, and that the name points back to the same address. Mail from an address with no reverse name is often treated as suspicious.
- Reading logs. A hostname says more at a glance than a bare address.
- Identifying a network. Provider hostnames frequently include a city code or the type of line.
What to make of the result
A reverse name is a claim by the address owner, not proof. Anyone who controls a block can publish any name there. A trustworthy check goes both ways: look up the returned hostname with the DNS Lookup tool and confirm it resolves back to the same address. For the network and country behind an address, use IP Lookup. More background is in what is DNS and how does it work.