IP to Hostname Lookup
Resolve an IP address back to the hostname registered for it using a reverse DNS (PTR) lookup, run from our EU servers.
About IP to Hostname Lookup
Forward DNS turns a name like mail.example.com into an IP address; reverse DNS does the opposite, turning an IP back into the name its owner has published for it. That name lives in a PTR record inside a special reverse zone: IPv4 addresses are looked up under in-addr.arpa with their octets reversed, and IPv6 addresses under ip6.arpa with their 32 nibbles reversed. This tool builds the correct reverse query name for the address you enter and resolves the PTR record from our EU infrastructure, returning the hostname that the address currently points back to.
Reverse DNS is more than a curiosity, it is an operational signal. Receiving mail servers routinely perform a reverse lookup on every connecting IP and treat a missing or generic PTR record as a spam indicator, so a sending IP whose reverse name is a meaningful mail host rather than an ISP-generated string is far more likely to be accepted. Reverse names also make logs, traceroutes and security tooling readable, replacing bare numbers with hostnames that reveal which network or service an address belongs to.
One important detail is who controls the answer. A PTR record is published by whoever administers the reverse zone for the address block, which is the ISP, hosting provider or network operator that owns the IP, not the owner of the forward domain. That is why the reverse name of an address often does not match its forward name, and why a lookup can legitimately return nothing at all: if no PTR record has been set for the address, there simply is no hostname to report. A robust check confirms this by comparing the reverse result with a forward lookup, a pairing known as forward-confirmed reverse DNS (FCrDNS).
Because a reverse lookup queries the DNS from a server rather than your own machine, this tool runs on our EU servers, sends the PTR query and returns the resulting hostname. It is a read-only operation that does not touch or probe the address itself; it only asks the DNS what name has been registered for it.
How to use it
- 1Enter the IPv4 or IPv6 address whose hostname you want to find.
- 2Run the lookup, which builds the reverse query name (in-addr.arpa for IPv4, ip6.arpa for IPv6) and resolves its PTR record.
- 3Read the returned hostname, or note that no PTR record is published if the result is empty.
- 4Optionally cross-check the hostname with a forward DNS lookup to confirm it resolves back to the same IP (forward-confirmed reverse DNS).
Common use cases
- -Checking that a mail server's sending IP has a proper PTR record before it starts sending, since missing reverse DNS is a common cause of rejected email.
- -Identifying the network or provider behind an IP seen in server logs, firewall alerts or an abuse report.
- -Making traceroute and monitoring output human-readable by turning bare addresses into hostnames.
- -Auditing whether the IPs you operate have correct and consistent reverse DNS entries.
- -Validating forward-confirmed reverse DNS (FCrDNS) as part of email deliverability or security hardening.
Frequently asked questions
- What is a reverse DNS (PTR) lookup?
- A reverse DNS lookup takes an IP address and returns the hostname its owner has published for it, stored in a PTR record. IPv4 addresses are queried under in-addr.arpa and IPv6 under ip6.arpa, with the address digits reversed.
- Why does an IP have no hostname?
- Because no PTR record has been created for it. Reverse records are optional and are set by the network operator that owns the address block; if they have not published one, the lookup correctly returns nothing.
- Why doesn't the hostname match the website's domain?
- The reverse (PTR) record is controlled by the owner of the IP address block, usually the ISP or hosting provider, not by the owner of the forward domain. As a result the reverse name is often a provider-generated hostname that differs from the site's own domain name.
- Why does reverse DNS matter for email?
- Receiving mail servers check the PTR record of every connecting IP and treat a missing or generic reverse name as a spam signal. A sending IP with a meaningful, forward-confirmed hostname is significantly more likely to have its mail accepted.
- What is the difference between forward and reverse DNS?
- Forward DNS resolves a hostname to an IP address using A or AAAA records, while reverse DNS resolves an IP address back to a hostname using PTR records. The two are configured independently and do not always agree; when they do, it is called forward-confirmed reverse DNS.