Reverse DNS Lookup by IP — online

This tool performs a Reverse DNS lookup: given an IP address it finds the associated hostname (PTR record). Both IPv4 and IPv6 are supported. Forward Confirmed rDNS (FCrDNS) is also verified.

What is a PTR record

A PTR (pointer) record lives in the reverse DNS zone and maps an IP address to a hostname. Unlike an A record (domain → IP), PTR works in the opposite direction: IP → domain. Reverse zones are .in-addr.arpa for IPv4 and .ip6.arpa for IPv6.

FCrDNS — what "confirmed" means

Forward Confirmed rDNS (FCrDNS) is an extra check: reverse DNS (IP → name) and forward DNS (name → IP) must return matching results. Mail servers and anti-spam systems use FCrDNS; messages from IPs with a mismatched PTR are frequently blocked or sent to spam.

Why you need Reverse DNS

• Mail server diagnostics — a valid PTR record is required for reliable email delivery;
• Identifying the hosting provider or ISP of an IP address;
• Analysing server logs (converting IP addresses to readable hostnames);
• FCrDNS verification when configuring an MTA (Postfix, Exim, Sendmail).