A reverse DNS lookup resolves an IP address back to its hostname using PTR DNS records — the opposite of a standard A record lookup. Use this tool to identify who owns an IP, verify email server hostnames, and check forward-confirmed reverse DNS (FCrDNS) status for email deliverability.
Reverse DNS Lookup
Enter any IPv4 or IPv6 address
Resolving PTR record...
No PTR record found
This IP address has no reverse DNS configured. The owner needs to add a PTR record through their ISP or hosting provider.
How to Use the Reverse DNS Lookup Tool
Reverse DNS lookup resolves an IP address to its hostname using PTR records — the opposite of the usual DNS lookup. This tool queries Cloudflare's DoH API to resolve the PTR record and then confirms it with a forward lookup (FCrDNS check).
Step 1: Enter an IP Address
Type any IPv4 address (e.g., 8.8.8.8) or IPv6 address (e.g., 2001:4860:4860::8888) in the input field. The tool automatically converts it to the correct PTR query format.
How PTR Records Work
IPv4 reverse DNS uses the .in-addr.arpa zone. The IP is reversed: 8.8.8.8 becomes 8.8.8.8.in-addr.arpa. IPv6 uses the .ip6.arpa zone with each nibble reversed separately.
Understanding FCrDNS
Forward-confirmed reverse DNS checks that the resolved hostname's A record points back to the original IP. A match means the IP, PTR record, and forward A record all agree — the strongest configuration for email server trust.
Common Use Cases
- Email server verification — check if your mail server IP has proper rDNS for deliverability
- Log analysis — convert server log IP addresses to readable hostnames
- Security investigation — identify the operator behind a suspicious IP
- Spam filter debugging — verify rDNS configuration when emails are rejected
- Network documentation — document server hostnames from IP inventory
FAQ
What is reverse DNS (rDNS)?
Reverse DNS lookup translates an IP address back to a hostname using PTR (pointer) records. While regular DNS maps names to IPs, reverse DNS goes the other direction. For IPv4, the IP is reversed and appended with .in-addr.arpa. For example, 8.8.8.8 becomes 8.8.8.8.in-addr.arpa, which resolves to dns.google.
What is forward-confirmed reverse DNS (FCrDNS)?
FCrDNS (also called full-circle rDNS) means the PTR record's hostname resolves back to the original IP. For example: 8.8.8.8 -> dns.google -> 8.8.8.8. If the forward lookup returns a different IP, it's a mismatch. FCrDNS is used by mail servers as an anti-spam measure — legitimate mail servers typically have matching forward/reverse DNS.
Why does reverse DNS matter for email?
Many spam filters check reverse DNS for incoming mail server IPs. If an IP has no PTR record, or if the PTR doesn't match the mail server's hostname (FCrDNS mismatch), the email may be marked as spam or rejected. Legitimate mail servers should have a PTR record matching their hostname, and that hostname's A record should resolve back to the IP.
Who controls reverse DNS for an IP?
Reverse DNS is controlled by whoever owns the IP block — typically your ISP or hosting provider, not the domain owner. To set a PTR record for your server's IP, you need to request it through your hosting provider or ISP. Cloud providers like AWS, Azure, and Google Cloud have self-service portals for setting reverse DNS.
Is this reverse DNS lookup tool free?
Yes, completely free. All lookups use Cloudflare's DNS over HTTPS API directly from your browser. No registration required and no queries are stored.
Does this support IPv6?
Yes, the tool supports both IPv4 and IPv6 addresses. IPv6 reverse DNS uses the ip6.arpa zone and requires reversing the full 128-bit address nibble by nibble. The tool automatically handles the conversion for any valid IPv4 or IPv6 address you enter.