DNS & EMAIL
Reverse DNS Lookup
Resolve an IP address back to its configured PTR hostname, or inspect PTR results for a hostname’s addresses.
39DExternal testRuns from the toolbox server
RUN TEST
Reverse DNS Lookup
HOW IT WORKS
About the Reverse DNS Lookup
Reverse DNS uses PTR records in special in-addr.arpa or ip6.arpa zones controlled by the address owner. Mail systems commonly compare forward and reverse records as one part of reputation checks.
How to use this result
- Run the test from this server.Use a public hostname, address, prefix or ASN in the format requested above.
- Compare with another observation point.Run a local command or use a second provider to identify location-specific behaviour.
- Correlate related evidence.Use the related tools below to compare DNS, routes, ports, TLS and application responses.
- Keep the time and context.Routing, DNS caches and reputation data change, so record when the result was collected.
Common interpretation issues
- The domain owner cannot normally set PTR directly unless they also control the IP allocation.
- A valid PTR does not guarantee that forward DNS points back to the same IP.
- IPv6 reverse zones are longer and must be delegated correctly.
NEED HELP INTERPRETING THE RESULT?
39D supports business networks, cyber security and managed IT.
For ongoing support or a larger infrastructure project, speak to the 39D team.
Frequently asked questions
Who changes reverse DNS?
Usually the ISP, hosting provider or LIR that assigned the IP address.
Does every IP need PTR?
Not for all uses, but public mail servers should normally have consistent forward and reverse DNS.