GLOSSARY · RDNS, PTR RECORD
Reverse DNS
Reverse DNS turns an IP address back into a name, the opposite of a normal lookup. The answer is stored in a PTR record, in a special zone: in-addr.arpa for IPv4 and ip6.arpa for IPv6, where the address is written backwards. The owner of the address block controls it.
Why it matters
A reverse name often reveals what the address is for. Names containing words like dsl, cable or dyn tend to be home connections, while names with server, vps or cloud suggest hosting. Mail servers also use reverse DNS as a trust signal: many refuse messages from addresses without a matching name. The record is optional and can say anything, so treat it as a hint.
In practice
To check an address, run a reverse lookup in the DNS lookup tool. Our VPN detector uses the reverse name as one weak signal among several and never as proof. If you run a mail server, ask your provider to set the PTR record to your mail host name, and make sure the name resolves back to the same address.
Related terms
- DNS: DNS is the internet's naming system.
- DNSBL: A DNSBL is a list of IP addresses, published through the DNS system, that an operator has marked as sources of spam or abuse.
- ASN: An ASN is a unique number assigned to a network that manages its own routing on the internet, such as an internet provider, a cloud company, a university or a large business.
- IP address: An IP address is a number that identifies a device or network connection on the internet, in the way a street address identifies a building.