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Find the Hostname for Any IPv4 Address
The Tools Kit’s free Reverse DNS Lookup turns an IP address back into a hostname. Enter an IPv4 address and the tool queries its PTR record, the DNS entry that says which name belongs to that address. It is the same rDNS check mail servers run on every incoming connection, and a quick way to identify the network behind an address in a server log.
You do not need to know the in-addr.arpa format or have a command-line tool such as dig or nslookup installed: the address is converted for you and the query is resolved on the site’s server. To go the other way, from a hostname to its addresses, use the DNS lookup tool. If you are not sure which public IP you are on right now, the IP address checker will show it.
How to Do a Reverse DNS Lookup
- 1
Enter an IPv4 address
Type the address in dotted form, for example 8.8.8.8. It must have four parts, each a number from 0 to 255; anything else is rejected before a query is sent.
- 2
Run the lookup
Press Enter or click Lookup. The tool reverses the four octets, appends in-addr.arpa and asks for the PTR record of that name.
- 3
Read the hostname
Each PTR record that comes back is listed on its own line. Most addresses have one, but more than one is valid.
- 4
Interpret an empty result
If the address has no reverse entry you will see "No PTR record found for this IP address." That is a real answer, not an error: many addresses simply have no PTR record.
The tool is free with no sign-up. Lookups go through a shared server endpoint, so a per-minute rate limit may slow you down if you run many queries in a row.
How PTR Records and in-addr.arpa Work
A forward lookup asks which address a name points to; an A record answers it. Reverse DNS asks the opposite question, and the answer lives in a separate place: a PTR record inside the special in-addr.arpa zone. To find it, the four octets of the address are written in reverse order and in-addr.arpa is added to the end.
| IPv4 address | Name queried | PTR result |
|---|---|---|
| 8.8.8.8 | 8.8.8.8.in-addr.arpa | dns.google |
| 1.1.1.1 | 1.1.1.1.in-addr.arpa | one.one.one.one |
| 203.0.113.25 | 25.113.0.203.in-addr.arpa | Whatever the block owner publishes, if anything |
The reversal is not arbitrary. Hostnames become more specific from right to left (google, then dns.google), while IP addresses become more specific from left to right. Flipping the octets lets a regional registry delegate 203.in-addr.arpa, and a provider delegate 113.0.203.in-addr.arpa for its own block, exactly the way subdomains are handed out. Those blocks follow network boundaries, which you can work out with the CIDR calculator.
This is also why you cannot set a PTR record from your domain’s DNS settings. Reverse zones belong to whoever holds the address block, so a custom reverse hostname has to be set by your ISP or hosting provider, usually through a support request or a field in its control panel.
Reverse DNS and Email Deliverability
The most common reason to check an rDNS record is email. Many receiving mail servers look up the PTR record of every connecting IP. A missing record, or a generic one like those assigned to home broadband, is a strong spam signal, and some servers reject the connection outright.
Stricter checks use forward-confirmed reverse DNS (FCrDNS): the PTR hostname must also resolve back to the same address. To test it, look up the IP here, then run an A record query for the returned hostname in the DNS lookup and confirm the addresses match. A healthy mail server also needs valid SPF, DKIM and DMARC records, which you can verify with the DMARC and SPF checker, and its IP should not appear on spam lists, which the blacklist checker tests.
Investigating an Unknown IP Address
When an unfamiliar address shows up in an access log, firewall alert or email header, the PTR hostname is often the fastest clue. Names like crawl-66-249-66-1.googlebot.com or a cloud provider’s compute hostname tell you who operates the address at a glance. Treat the result as a hint rather than proof: the block owner chooses the PTR value, so it should be confirmed with a forward lookup before you trust it.
When the hostname points to a domain you want to know more about, the WHOIS lookup shows its registration details. If the address came from a sign-up or contact form, pairing reverse DNS with the email validator helps you judge whether the submission looks genuine.
Common uses
- Checking that a mail server’s IP has the PTR record email delivery depends on
- Confirming reverse DNS after a hosting provider sets it up for you
- Identifying the network or company behind an address in a server or firewall log
- Verifying that a crawler claiming to be a search engine really comes from its network
- Translating the IPs in email headers or traceroute output into readable hostnames
For more DNS, network and encryption utilities, browse all security tools.
Reverse DNS terms explained
| Term | What it means |
|---|---|
| Reverse DNS (rDNS) | Resolving an IP address back to a hostname, the opposite of a normal forward lookup |
| PTR record | The DNS record type that holds the hostname for an address; it is what this tool queries |
| in-addr.arpa | The special DNS zone for IPv4 reverse lookups; the address is written backwards in front of it |
| ip6.arpa | The equivalent zone for IPv6, which uses a reversed nibble format; not supported by this tool |
| A record | A forward record that maps a hostname to an IPv4 address |
| FCrDNS | Forward-confirmed reverse DNS: the PTR hostname resolves back to the same IP address with an A record |
Frequently Asked Questions
A reverse DNS lookup finds the hostname registered for an IP address. A normal DNS lookup goes from a name such as dns.google to an address; a reverse lookup goes from an address such as 8.8.8.8 back to a name by querying the address’s PTR record.
Enter the IPv4 address and click Lookup. The tool turns the address into its in-addr.arpa name, queries the PTR record and lists any hostname it finds. For 8.8.8.8 the PTR record is dns.google, and for 1.1.1.1 it is one.one.one.one.
A PTR (pointer) record maps an IP address to a hostname. It lives in a special reverse zone: the address’s octets are written in reverse order and in-addr.arpa is added, so the PTR record for 8.8.8.8 is stored at 8.8.8.8.in-addr.arpa and the one for 203.0.113.25 at 25.113.0.203.in-addr.arpa.
Domain names get more specific from right to left, while IP addresses get more specific from left to right. Reversing the octets lines the two up, so an ISP or hosting company can be delegated the reverse zone for its own address block in the same way a subdomain is delegated.
Reverse DNS is controlled by whoever owns the address block, usually your ISP or hosting provider, not by the owner of a domain. Many home, mobile and cloud addresses have no PTR record or only a generic one. To set a custom hostname you have to ask the provider or use its control panel.
Many receiving mail servers check that the connecting IP address has a PTR record, and often that the hostname resolves back to the same address. Mail from an address with missing or mismatched reverse DNS is more likely to be rejected or sent to spam.
Yes. An address can have several PTR records, although most have exactly one, and many mail systems expect a single, consistent name. The tool lists every PTR record that comes back rather than only the first.
No. Only IPv4 addresses in dotted form are accepted. IPv6 reverse lookups use the ip6.arpa zone, where the address is expanded into 32 hexadecimal digits written in reverse, and that format is not handled here.
The in-addr.arpa name is built in your browser, then the PTR query is made by the site’s server, which resolves it recursively through Google Public DNS at 8.8.8.8. Answers can be cached for a short time, so a record you have just changed may take a little while to show up.
Usually nothing. Private ranges such as 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are only named inside local networks, and public resolvers like Google Public DNS do not hold PTR records for them, so you will normally see the no record message.
No. Reverse DNS returns only the hostname the network operator has published for an address. WHOIS returns registration details for a domain. They are often used together when investigating an unfamiliar address.
Reviewed by Raja Jahangir · Last reviewed: October 7, 2026
How do you find the hostname for an IP address?
To find the hostname behind an IPv4 address, enter the address and a PTR lookup runs. The four octets are reversed and appended to in-addr.arpa, so 8.8.8.8 becomes 8.8.8.8.in-addr.arpa, and Google's 8.8.8.8 resolver is queried for the PTR record; for 8.8.8.8 the answer is dns.google. Only IPv4 addresses are supported.
Why does an IP address have no PTR record?
A PTR record only exists if the owner of the IP block publishes one, and many home and cloud addresses never get one. Reverse DNS is controlled by the network operator, not the domain owner, so a missing record is common. Mail servers should have one, because receiving servers often reject mail from addresses without a PTR record.