Reverse DNS lookup
Reverse DNS lookup: enter an IP address to find its hostname and see whether forward and reverse DNS match.
Queries go to Cloudflare’s public DNS over HTTPS service when you press the button.
About the reverse dns lookup
Reverse DNS lookup: enter an IP address to find its hostname and see whether forward and reverse DNS match.
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How to use the reverse dns lookup
What it calculates and when to use it
Finds the hostname that belongs to an IP address using its reverse DNS (PTR) record, and checks that the hostname resolves back to the same address, which is called forward-confirmed reverse DNS. Mail servers use this check to decide whether to trust a sender.
How to use it, step by step
- Enter an IP address, or leave the box empty to use your own.
- Press “Find hostname”.
- Read the hostname at the top.
- Check “Forward-confirmed” to see whether the name resolves back to the address.
What each input means
- IP address – An IPv4 or IPv6 address. Leave it empty to use your own public address.
How to read the results
- Hostname – The name set in the address’s PTR record.
- Reverse name – The special name queried, such as 8.8.8.8.in-addr.arpa.
- Forward-confirmed – Yes when the hostname’s A or AAAA record points back to the same address.
The formula
The address is reversed and queried under in-addr.arpa for IPv4, or ip6.arpa with each hex digit reversed for IPv6. 8.8.4.4 becomes 4.4.8.8.in-addr.arpa. The returned name is then looked up forward to confirm it.
A worked example
8.8.8.8 has the PTR record dns.google, and dns.google resolves back to 8.8.8.8, so the pair is forward-confirmed.
Assumptions and limits
- Many addresses, especially home connections, have no PTR record or a generic one.
- The lookup is made through Cloudflare’s DNS over HTTPS service when you press the button.
Common mistakes
- Expecting every address to have a hostname.
- Treating the hostname as proof of identity. The owner of the address sets it, so only forward-confirmed names add trust.
- Setting a PTR record at your domain registrar. It is set by whoever holds the IP address block, usually your hosting or internet provider.
Frequently asked questions
What is a PTR record?
A DNS record that maps an IP address back to a hostname. It is the reverse of an A record.
Why does my mail server need reverse DNS?
Many receiving mail systems reject or flag mail from addresses with no reverse DNS or one that does not match.
Who can change a PTR record?
The organisation that controls the IP address block, normally your hosting provider or ISP.
Is this the same as a hostname lookup?
Yes. Finding the hostname of an IP address is done with reverse DNS.