Reverse DNS
Look up the hostname registered for a public IP. Use it when reading connection logs or checking mail-server PTR records.
Quick start
- Enter a public IP.
- Read the PTR hostnames.
- Compare their A or AAAA records if needed.
Who controls a PTR record?
PTR records belong to reverse DNS zones. They are usually configured by the IP provider or a delegated reverse-zone administrator. Changing a domain’s A record does not change its PTR.
Interpret the result
| Result | Meaning |
|---|---|
| A hostname is returned | The name is registered in reverse DNS. It does not prove ownership or safety. |
| No PTR | This is not necessarily a web connectivity error. Requirements depend on the service. |
| Forward and reverse records disagree | Check whether the PTR name resolves back to the original IP. |
Mail and bot verification
Mail receivers may consider PTR and forward consistency as part of reputation checks. They do not guarantee delivery or removal from spam lists. Verify bots against the provider’s documented domain and IP checks.
PPORT caches PTR results for up to 10 minutes. This tool does not automatically complete forward-confirmed reverse DNS verification.
Looking up a PTR record yourself
Use Resolve-DnsName in Windows PowerShell, or dig -x on Linux and macOS. The output below looks up the PTR of Google Public DNS at 8.8.8.8, then checks that the A record of the returned name points back to the original IP.
PS> Resolve-DnsName -Name 8.8.8.8 -Type PTR | Select-Object Name,NameHost
Name NameHost
---- --------
8.8.8.8.IN-ADDR.ARPA dns.google
PS> Resolve-DnsName -Name dns.google -Type A | Select-Object Name,IPAddress
Name IPAddress
---- ---------
dns.google 8.8.4.4
dns.google 8.8.8.8dig -x 8.8.8.8 +short
dig +short dns.google AThe A records of the PTR name dns.google include the original address 8.8.8.8, so the forward and reverse lookups match.
How reverse lookup names are built
For IPv4, the octets are reversed and in-addr.arpa is appended. For 203.0.113.25 the resolver looks for the PTR record of 25.113.0.203.in-addr.arpa. For IPv6, the address is reversed one hexadecimal digit at a time under ip6.arpa.
This zone is managed by whoever was assigned the IP address, not by the domain owner, so you cannot create a PTR record in your domain’s DNS settings.
Verifying a search engine crawler
- Find the IP of the request that claims to be a crawler in your access log.
- Look up the PTR name of that IP. For Googlebot it must end in googlebot.com, google.com or googleusercontent.com.
- Look up the A and AAAA records of that name and check that the original IP is returned. Only when both lookups match can you treat it as Google’s crawler.