Reverse DNS and PTR
What Reverse DNS Does
Reverse DNS is the lookup that turns an IP address back into a hostname. Normal DNS answers the question, which address belongs to this name? Reverse DNS answers the opposite: which name belongs to this address? The answer is stored in a PTR record, short for pointer record. The addresses themselves are explained in what an IP address is.
Reverse lookups are used by logging tools, diagnostic utilities and some network services that want a readable name for a connecting address. A reverse record is optional for most websites, but it helps when a server's address should be identified clearly.
How Reverse Zones Are Organized
Reverse records live in special zones. For IPv4, the zone is in-addr.arpa, and the address is written with its four octets reversed. For IPv6, the zone is ip6.arpa, and the address is written as reversed hexadecimal digits, one per label. A PTR record at the reversed name gives the hostname:
10.2.0.192.in-addr.arpa. 3600 IN PTR server.example.com.
Reversing the address puts the broad network part nearest the root of the reverse tree, so delegation can follow the same blocks that IP addresses are assigned in. The host part sits at the left, where the most specific labels are.
Who Controls a Reverse Record
The reverse zone is delegated to whoever holds the IP address block, usually an internet service provider, data center or hosting company. That is why a domain owner cannot set a PTR record in their own DNS zone. The record must be created by the party that controls the address, through their control panel or support process.
On shared hosting, the provider often sets one reverse name for a whole server and shares it across many sites. With a dedicated address, the account holder may be able to request a custom PTR value, such as a name that matches their mail or web server. For how these records relate to the choice of address type, see dedicated vs shared IP addresses.
A common check is forward-confirmed reverse DNS, where the PTR name also resolves forward to the same address. Some services use this check, but its details belong to the email category.
Frequently asked questions
Why Can't I Set Reverse DNS in My Domain's Zone?
Reverse DNS is controlled by the owner of the IP address, not by the domain. The PTR record sits in a reverse zone delegated along the address block, not in your domain's zone. Ask the party that manages the IP address, often your hosting provider, to set it.
Can an IP Address Have More Than One PTR Record?
DNS allows more than one PTR record at the same reverse name, but most setups use one. Clients expect a single, clear hostname for an address, and extra values can confuse tools that read only the first answer. If you need several names for one address, a single PTR record and correct forward records are usually the cleaner choice.