Reverse DNS lookup
Find the hostname behind an IP address, and check that it points back.
Results for 1.1.1.1
PTR record found
one.one.one.one
The reverse record for 1.1.1.1 points to one.one.one.one, and that name points straight back. Mail servers like that.
one.one.one.one → 1.1.1.1
TTL 1,009 s · asked cloudflare
Where this record lives · answered in 31 ms
Names1
| Name | TTL |
|---|---|
| one.one.one.one | 1,009 s |
Forward check1
Each name is looked up again, to see whether it leads back to this address. That is what mail servers and bot checks rely on.
| Name | Resolves to | Points back |
|---|---|---|
| one.one.one.one | 1.0.0.11.1.1.1 | Yes |
Structured result (JSON) · 531 B
{
"ip": "1.1.1.1",
"version": 4,
"arpa": "1.1.1.1.in-addr.arpa",
"status": "found",
"rcode": "NOERROR",
"hostnames": [
{
"name": "one.one.one.one",
"ttl": 1009
}
],
"forwardConfirm": {
"status": "confirmed",
"checked": [
{
"hostname": "one.one.one.one",
"addresses": [
"1.0.0.1",
"1.1.1.1"
],
"matches": true,
"rcode": "NOERROR"
}
]
},
"resolver": "cloudflare",
"ms": 31,
"notes": [],
"minTtl": 1009
}What reverse DNS is
Reverse DNS (rDNS) finds the hostname behind an IP address. The hostname is stored in a PTR (pointer) record, the mirror image of the A and AAAA records that turn names into addresses. LookupOwl then checks that the name points back to the same address, a test known as forward-confirmed reverse DNS (FCrDNS).
PTR records live in two special zones, in-addr.arpa for IPv4 and ip6.arpa for IPv6, and whoever owns the block of addresses that IP belongs to controls them. That is usually your ISP or hosting provider, not the owner of the domain. To look up 8.8.4.4, the address is written backwards as 4.4.8.8.in-addr.arpa and a PTR query is sent. IPv6 works the same way with one hex digit per label, and the IPv6 expander will show you the name for any address.
How to use it
- Enter an IP addressIPv4 or IPv6, written out in full or shortened. A full
in-addr.arpaname or a URL that contains an address works too. Private addresses such as192.168.1.10have no public reverse record, so LookupOwl turns them down with an explanation instead of querying them. - Read the PTR nameAn address can have none, one or several names. For a mail server, the name you want to see is a stable one that you control, like
mail.example.com. - Check that it points backLookupOwl looks up each name it found (the first five) for an A record, or AAAA for IPv6, and checks that the original address is among the answers. The result reads Forward-confirmed, Partly confirmed or Not confirmed, or Unverified if those lookups got no answer. Many mail servers want a confirmed result. To skip the check, switch off Verify the name resolves back in More options.
What a good PTR looks like
| Result | What it tells you |
|---|---|
| PTR matches the server's name, and the name resolves back to the IP | Healthy FCrDNS. Good for mail servers and for tools that log by hostname. |
| PTR exists but the name resolves elsewhere | Not forward-confirmed. Mail from this IP may be rejected or filed as spam. |
| Some names confirmed, some not | Partly confirmed. Remove the names that don't resolve back. |
Generic PTR such as 203-0-113-7.dyn.isp.example | A default name an ISP gives to home or dynamic addresses. Many mail systems distrust these. |
| No PTR | The owner has not set one. Common on home connections and new cloud servers. |
| Several PTRs | Allowed, but mail systems treat them inconsistently. Keep one. |
Why rDNS matters and how to fix it
- Email delivery. If your outgoing mail is bouncing or landing in spam, check the PTR first, then your SPF and DMARC records. Gmail's sender guidelines ask for valid forward and reverse DNS on the sending IP.
- Forward and reverse don't match. After you set a PTR to
mail.example.com, make suremail.example.comhas an A (or AAAA) record with the same IP. - Your provider has delegated the block to you. Then you run the reverse zone on your own nameservers. For blocks smaller than a /24, the delegation uses the classless method in RFC 2317.
- A change isn't visible yet. Reverse records are cached like any other DNS record, so wait for the TTL. The result shows it as Cached for.
- “We couldn't check” or an error. The nameservers for that address block did not answer properly. That is on the owner's side. Try again in a minute.
How the lookup works
LookupOwl turns the address into its reverse name and asks Cloudflare's public resolver for PTR records (type 12). It then looks up each name it got, up to five, for A or AAAA records and checks that the original address is in the answer. Private, reserved and special-purpose addresses are turned away before any query is sent. Results are cached for 30 seconds to 5 minutes, and Check again fetches a fresh one.
dig -x 8.8.8.8 +short
dig -x 2001:4860:4860::8888 +short
nslookup 8.8.8.8
host 1.1.1.1
# Then check that the name points back
dig +short A dns.googleStandards: RFC 1035 (PTR and in-addr.arpa), RFC 3596 (ip6.arpa), RFC 2317 (classless delegation) and RFC 1912 (common DNS errors, including a missing PTR).
Questions people ask
What is a PTR record?
A PTR record is a DNS record that maps an IP address to a hostname, the reverse of what an A or AAAA record does. It is published by whoever owns the IP block, and one address can have none, one or several of them. The hostname is only a claim by that owner, which is why LookupOwl checks that the name points back.
What is forward-confirmed reverse DNS?
Forward-confirmed reverse DNS (FCrDNS) is a two-step check. The IP's PTR record gives a hostname, and that hostname's A or AAAA record must give the same IP. It shows that whoever controls the address also controls the name, which is why mail servers and bot checks lean on it.
Who controls the reverse DNS of an IP?
The organisation that owns the address block, normally your ISP or hosting company. Domain owners cannot change it from their DNS panel unless the block has been delegated to them, which is why your registrar or DNS host usually cannot help with it.
How do I set or change a PTR record?
Ask whoever gives you the IP address, such as your hosting provider, cloud console or ISP. Many have a reverse DNS or rDNS field next to the server's IP. Enter the hostname you want, make sure that hostname has an A or AAAA record for the same IP, then check here once the old record's TTL has passed.
Why does my mail server need a PTR record?
Many receiving servers use it as a basic sign of a legitimate sender. A missing or mismatched PTR can lead to rejection or delivery to the spam folder. It is one check among several, alongside SPF, DKIM and DMARC, and it is cheap for a receiving server to run.
Can an IP have more than one PTR record?
Yes, but it is best to keep one. Software handles multiple records inconsistently, and some mail checks fail if there is more than one. LookupOwl lists up to 20 names, checks the first five and adds a note when it finds more than one.
How is this different from IP WHOIS?
WHOIS says who the address block is registered to. Reverse DNS gives the hostname the owner chose to publish for one address, which can hint at the provider or the role of the machine. Use both together: the IP WHOIS lookup shows the owner, and this page shows the name.
Use it from AI, the API or the command line
Every LookupOwl tool is also a free API and an MCP tool, with no key and no account. This one is reverse_dns. Please be kind to the rate limits.
curl "https://lookupowl.com/api/v1/tools/reverse-dns?q=8.8.8.8"claude mcp add --transport http lookupowl https://lookupowl.com/mcp