NETWORK UTILITY

FCrDNS Checker

Go beyond a basic PTR lookup by verifying that reverse DNS resolves forward to the original IP.

Forward-Confirmed Reverse DNSPTR + forward check

What is FCrDNS?

Forward-confirmed reverse DNS starts with an IP address, finds its PTR hostname, then resolves that hostname forward again. Verification succeeds when the original IP appears in the forward A/AAAA results.

FCrDNS does not prove identity. It only demonstrates consistency between reverse and forward DNS for the address at the time of the test.

Why it is more useful than PTR alone

A PTR record can point to a hostname that does not resolve back to the original address. FCrDNS makes that mismatch visible and is commonly useful when diagnosing mail, hosting and network configuration.

Where FCrDNS is useful

Forward-confirmed reverse DNS is commonly used as a consistency check in mail infrastructure and network diagnostics. It can help distinguish a well-configured server hostname from a PTR record that no longer resolves back to the address.

Verification is not authentication

A verified FCrDNS relationship only proves that the current reverse and forward DNS records are mutually consistent. It does not prove the identity of a person, guarantee that a mail sender is trustworthy or establish ownership of every service on the IP.

What to check after a mismatch

If the PTR exists but the hostname does not resolve back to the original IP, review the reverse-DNS provider, A/AAAA records and recent infrastructure changes. DNS caching can also create short-lived inconsistencies after updates.