What is a reverse DNS lookup?

Normal DNS turns a name into an IP address. Reverse DNS does the opposite: it starts with an IP address and asks which hostname belongs to it. The answer is stored in a PTR record, which the owner of the address publishes.

For example, looking up 8.8.8.8 returns dns.google.

What is reverse DNS used for?

• Email delivery: many mail servers distrust messages from an address without a matching reverse DNS record, so mail administrators check this first.
• Reading logs: a hostname says more about a visitor or a scanner than a bare number.
• Network troubleshooting: hostnames from providers often hint at the network or region of an address.
• Spotting crawlers: large search engines publish hostnames that help you confirm a crawler is genuine.

Why is there no result?

Reverse DNS records are optional, so plenty of addresses have none. That says nothing about whether an address is safe, active, or in use.

Private addresses, such as those starting with 192.168, have no public record at all. Only a DNS server inside that network can answer for them. Read more in what an IP address is.

Does a hostname prove who owns an address?

No. The owner of an address can publish any name in a PTR record, including a name they do not control. To confirm a hostname, look up its normal DNS record and check that it points back to the same IP address.

Can I change my own reverse DNS record?

Only the party that controls the address can change it. For a home connection that is your internet provider. For a server, you can usually set it in the control panel of your hosting company.