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Utility #9Node.js FCrDNS
Reverse DNS (PTR) Lookup & FCrDNS Test
Resolve any IPv4 or IPv6 address to its registered PTR hostnames, test Forward-Confirmed Reverse DNS, and verify email sender reputation in real time.
Try public recursive resolvers:
Reverse DNS Architecture & in-addr.arpa
Reverse DNS delegates authority backward through reversed IP octets to establish authentic host identity across the global Internet.
1. Octet Reversal
An IP like 1.2.3.4 is queried as 4.3.2.1.in-addr.arpa following hierarchical DNS tree traversal.
2. Mail Sender Reputation
Spam filters correlate the SMTP HELO/EHLO banner with the PTR hostname and matching forward A record before accepting message transmission.
3. IPv6 ip6.arpa Structure
IPv6 addresses are fully expanded into 32 individual nibble hex characters separated by dots under the ip6.arpa domain.
Frequently Asked Questions About Reverse DNS
Technical answers regarding PTR record setup, mail deliverability, and ISP delegation.
While standard forward DNS maps a domain name to an IP address (e.g., example.com ➔ 93.184.216.34), Reverse DNS (rDNS) does the exact opposite: it queries the special in-addr.arpa (IPv4) or ip6.arpa (IPv6) root zone to discover the registered domain hostname associated with that IP address.
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