1. IP Reversal: The IP octets are reversed
192.168.1.1 → 1.1.168.192
2. Zone Append: Added to in-addr.arpa
1.1.168.192.in-addr.arpa
3. PTR Query: DNS returns hostname
PTR records will appear here
Enter IP address(es) and click Reverse DNS Lookup| IP Address | Hostname(s) | Duration |
|---|
-x 8.8.8.88.8.8.88.8.8.8Every coffee helps keep the servers running. Every book sale funds the next tool I'm dreaming up. You're not just supporting a site — you're helping me build what developers actually need.
Reverse DNS (rDNS) is a DNS lookup that resolves an IP address to its associated hostname. Unlike forward DNS that translates domain names to IP addresses, reverse DNS does the opposite. It uses PTR (Pointer) records stored in special zones like in-addr.arpa (IPv4) or ip6.arpa (IPv6).
Most mail servers check reverse DNS to verify sender legitimacy. Missing or mismatched PTR records often result in emails being rejected or marked as spam.
Web servers and network devices use reverse DNS to log hostnames instead of IP addresses, making logs more readable and easier to analyze.
FCrDNS is a security verification where the reverse DNS hostname must also resolve back to the original IP address. This two-way verification helps prevent IP spoofing and is commonly required by email servers.
| Check | Description | Example |
|---|---|---|
| Step 1 | Reverse lookup: IP → Hostname | 8.8.8.8 → dns.google |
| Step 2 | Forward lookup: Hostname → IP | dns.google → 8.8.8.8 |
| Result | If both match, FCrDNS passes | Verified sender |