IPv4 Reverse DNS (in-addr.arpa) Generator
Enter an IPv4 address to build its in-addr.arpa reverse-DNS pointer name. The octets are reversed and given the .in-addr.arpa suffix — exactly the name a resolver uses to find a PTR record.
0–255, separated by dots.
Every normal DNS lookup turns a name into an address. Reverse DNS does the opposite, turning an address back into a name via a PTR record. To make that fit the DNS hierarchy, IPv4 addresses get their own special domain: in-addr.arpa.
The construction is simple. Take the four octets of the address, reverse their order, join them with dots and append .in-addr.arpa. So 192.0.2.1 becomes 1.2.0.192.in-addr.arpa. The reversal exists because DNS reads names from most specific (left) to least specific (right), whereas IP addresses are written the other way around — flipping the octets lines the two hierarchies up so address blocks can be delegated just like domains.
Mail servers frequently check that a sending IP has a matching PTR record before accepting messages, and PTR records make logs, traceroutes and diagnostics far more readable. A missing or generic reverse record is a common reason legitimate mail gets flagged as spam.
This generator only builds the name — it performs no lookup, and nothing you type ever leaves your browser, so it is safe for internal ranges. It is ideal when you are writing a reverse zone file or delegating a block and need the exact label order. To understand how PTR records work end to end, read reverse DNS and PTR records. For the IPv6 equivalent, use the IPv6 Reverse DNS generator, and to query a live PTR record, try the Reverse DNS Lookup tool.
Frequently asked questions
What is an in-addr.arpa name?
in-addr.arpa is the special domain used for IPv4 reverse DNS. You take the four octets of an address, write them in reverse order, and append .in-addr.arpa. For 192.0.2.1 the reverse name is 1.2.0.192.in-addr.arpa.
Why are the octets reversed?
DNS names are read from most specific on the left to least specific on the right, but IP addresses are written most significant first. Reversing the octets lets the address fit the DNS hierarchy, so blocks can be delegated the same way domains are.
How do I add a PTR record?
Generate the in-addr.arpa name, then create a PTR record in the reverse zone that maps it to your hostname. The reverse zone for your address range is usually delegated to you or your ISP by the registry that owns the block.
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