Reverse IP Lookup
Resolve any IPv4 or IPv6 address back to its hostname by looking up the PTR record in reverse DNS.
About Reverse IP Lookup
Reverse IP Lookup answers the opposite question to an ordinary DNS lookup: instead of finding the address behind a name, it finds the name behind an address. Given an IP, it queries the PTR (pointer) record that maps that address back to a hostname. This is the reverse DNS half of the naming system, and it is what turns an anonymous number like 62.129.0.5 into a meaningful hostname such as mail.example.eu.
Reverse DNS uses a special query name rather than the address itself. For IPv4, the four octets are reversed and placed under the in-addr.arpa zone; for IPv6, the address is expanded to its 32 hexadecimal nibbles, reversed, and placed under ip6.arpa. This tool builds that query name for you automatically from either address family and shows it alongside the result, so you can see exactly what was asked as well as the hostname or hostnames returned. If the address has no PTR record, it tells you plainly rather than leaving you guessing.
The most common reason reverse DNS matters is email deliverability. Receiving mail servers routinely check that a sending server's IP has a valid PTR record, and ideally one that matches its forward hostname, as a basic anti-spam signal; a missing or generic PTR is a frequent cause of legitimate mail being flagged or rejected. Beyond mail, reverse lookups help you identify the operator of an IP seen in server logs, verify that a host is configured as expected, and add readable names to network diagnostics and traceroutes.
Reverse DNS is controlled by whoever administers the IP block, typically your hosting provider or ISP, not by the owner of the forward domain, which is why an address you control may still have no PTR or a provider-default one. Both IPv4 and IPv6 are fully supported here, and the lookups run server-side from our EU infrastructure. It pairs well with the forward DNS tools when you want to confirm that an address and its hostname agree in both directions.
How to use it
- 1Enter the IP address you want to resolve, either IPv4 (for example 62.129.0.5) or IPv6.
- 2Select the lookup button to query the corresponding PTR record.
- 3Read the returned hostname, or the note that the IP has no reverse DNS entry.
- 4Note the generated PTR query name shown above the result, ending in in-addr.arpa for IPv4 or ip6.arpa for IPv6.
- 5For mail servers, cross-check the returned hostname against the address's forward A or AAAA record to confirm they match.
Common use cases
- -Diagnosing email deliverability by confirming a sending mail server's IP has a valid, matching PTR record.
- -Identifying the host or operator behind an IP address found in server logs, firewall alerts or access records.
- -Verifying that a newly provisioned server or mail relay has the reverse DNS entry you requested from your provider.
- -Adding readable hostnames to network troubleshooting, such as interpreting the hops in a traceroute.
- -Checking reverse DNS for both IPv4 and IPv6 addresses when validating a dual-stack deployment.
Frequently asked questions
- What is a PTR record?
- A PTR (pointer) record maps an IP address to a hostname, providing the reverse of a normal DNS lookup. It lives in the in-addr.arpa zone for IPv4 addresses and the ip6.arpa zone for IPv6, and is the record a reverse DNS lookup retrieves.
- What is reverse DNS used for?
- Reverse DNS is most often used to check the reputation of mail servers: receiving servers verify that a sending IP has a valid PTR record before accepting mail. It is also used to identify hosts in logs, label traceroute hops, and confirm that servers are named as expected.
- Why does an IP address have no PTR record?
- Reverse DNS for an IP is set by whoever controls the address block, usually the hosting provider or ISP, not the domain owner. If they have not configured a PTR record for that address, a reverse lookup returns nothing, which is common for residential and unconfigured addresses.
- How is reverse DNS different from forward DNS?
- Forward DNS resolves a hostname to an IP address using records like A and AAAA. Reverse DNS does the opposite, resolving an IP address back to a hostname using a PTR record. The two are configured independently and do not have to match, though for mail servers they should.
- Does reverse lookup work for IPv6 addresses?
- Yes. IPv6 addresses are supported: the address is expanded to its full 32 nibbles, reversed, and queried under the ip6.arpa zone. You can enter an IPv6 address the same way you would an IPv4 one and the correct query name is built for you.
- Should a mail server's PTR match its hostname?
- Ideally yes. Best practice is for a mail server's IP to have a PTR record whose hostname also resolves back to that same IP (forward-confirmed reverse DNS). A missing or mismatched PTR is a common reason legitimate mail is marked as spam or rejected.