What is reverse DNS?

Normal DNS turns a name into an IP address. Reverse DNS goes the other way: it turns an IP address into a hostname. The owner of an address publishes the hostname as a PTR record under a special name built from the address backwards, such as 8.8.8.8.in-addr.arpa for 8.8.8.8, or the 32 hex digits of an IPv6 address reversed under ip6.arpa.

Tool description

Enter an IP address and press Look up hostname. You get the PTR record name the lookup used and every hostname the address points to.

For each hostname, Points back to the IP says whether the hostname's own A (IPv4) or AAAA (IPv6) records include the address again. When they do, the address has forward-confirmed reverse DNS (FCrDNS). Mail servers check this before accepting email, so a sending server without it often ends up in spam.

The lookup runs on our server through Google Public DNS. The IP address itself is never contacted.

AI assistants connected to the Rapid Tool Set MCP server can run the same lookup as reverse_dns_lookup.

Examples

  • 8.8.8.8 points to dns.google, which points back to it
  • 1.1.1.1 points to one.one.one.one
  • An address of a home connection usually points to a name the internet provider generated from the address

Tips

  • Many cloud and home addresses have no PTR record at all; that isn't an error.
  • The PTR record is set by whoever controls the address block (your hosting or internet provider), not in your domain's DNS zone. Ask them to set it if your mail server needs one.