What a reverse DNS lookup shows you

A reverse DNS lookup is the opposite of a standard DNS query. Instead of translating a domain name into an IP address, it works backward. A reverse IP lookup resolves an IP address back to its hostname. This is done through PTR records (Pointer records), a special type of DNS record stored in a dedicated reverse zone. When you run a PTR record lookup, the resolver queries that reverse zone. It returns the hostname assigned to the IP. The hostname is set by the IP’s owner or internet service provider. For a full explanation of the concept, see our article on what is reverse DNS.

How the in-addr.arpa domain works

IPv4 reverse DNS relies on a cleverly designed namespace called in-addr.arpa. To look up the PTR record for an IPv4 address, the four octets are reversed and appended with “.in-addr.arpa”. For example, a reverse lookup on 8.8.8.8 means querying the domain 8.8.8.8.in-addr.arpa. This reversal is needed because the DNS hierarchy reads from right to left. The most significant label sits on the right. Reversing the octets makes the in-addr.arpa tree mirror the structure of IP address allocation. That lets DNS servers delegate reverse zones just as they delegate forward zones for domain names. Learn more about the full resolution process in our guide on how DNS works.

IPv6 reverse DNS: the ip6.arpa zone

IPv6 addresses use a parallel reverse zone called ip6.arpa, built the same way but at much finer granularity. The address is first expanded to its full 32 hexadecimal digits. So 2001:4860:4860::8888 becomes 2001:4860:4860:0000:0000:0000:0000:8888. Every hex digit is then reversed and separated by dots before appending “.ip6.arpa”. The resulting query domain is long, but the per-digit “nibble” format lets reverse zones be delegated along any 4-bit boundary. That matches how IPv6 space is allocated. This tool handles the expansion and nibble formatting automatically for any IPv6 address you paste.

Why reverse DNS matters

Reverse DNS lookups serve several critical purposes across networking, security, and email infrastructure:

• Email deliverability: Since February 2024, Google and Yahoo require sending IP addresses to have valid PTR records. The hostname must resolve back to the same IP, known as forward-confirmed reverse DNS (FCrDNS). Mail from IPs that fail the check is increasingly rejected outright, and Gmail tightened enforcement further in late 2025. Microsoft and Apple apply similar rules, making reverse DNS a baseline requirement alongside SPF, DKIM, and DMARC.
• Security investigation: When analyzing server logs, firewall alerts, or intrusion attempts, security teams turn to reverse IP lookups. They identify the hostnames behind suspicious addresses. This helps trace the origin of attacks. It also shows whether traffic comes from known hosting providers, botnets, or legitimate services.
• Network troubleshooting: Network administrators rely on reverse DNS to verify that IP assignments are configured correctly. Tools like traceroute display PTR hostnames at each hop. That makes it much easier to see which routers and networks traffic passes through on its way to a destination. See our network troubleshooting guide for more techniques.

This tool queries Google Public DNS in real time. It builds the correct in-addr.arpa or ip6.arpa domain from the address you provide and returns every PTR record found. Whether you are diagnosing email delivery, investigating a suspicious IP, or verifying your own server’s setup, the tool covers it. Results arrive in seconds. No installs, no signups.

Reverse DNS FAQ

What is a PTR record?

A PTR (Pointer) record is the DNS record that maps an IP address back to a hostname. It is the reverse of an A or AAAA record. PTR records live in dedicated reverse zones: in-addr.arpa for IPv4 and ip6.arpa for IPv6. They are managed by whoever controls the IP address, typically an ISP or hosting provider.

Why does my IP address have no PTR record?

Reverse DNS is configured by the owner of the IP address range, not the person using the IP. Many residential ISP addresses have only a generic auto-generated PTR record or none at all. Cloud and hosting IPs start without one until you set it in your provider’s control panel. A missing PTR record is normal for home connections but a problem for mail servers.

How do I set up reverse DNS for my IP address?

You cannot create a PTR record in your own domain’s DNS settings. The reverse zone belongs to whoever allocated the IP. For cloud and hosting providers, look for a reverse DNS or PTR field. You will find it in the control panel where the IP is managed. For a dedicated IP from an ISP, you typically request the PTR record through support. The hostname you set should also resolve back to the same IP, which is forward-confirmed reverse DNS.

Why does email delivery depend on reverse DNS?

Since February 2024, Google and Yahoo require sending IP addresses to have valid PTR records. The PTR hostname must also resolve back to the same IP, known as forward-confirmed reverse DNS. Mail from IPs that fail this check is increasingly rejected outright, with Gmail tightening enforcement further in late 2025. Microsoft and Apple apply similar requirements, making a valid PTR record a baseline for deliverability alongside SPF, DKIM, and DMARC.

Does reverse DNS work for IPv6 addresses?

Yes. IPv6 reverse DNS uses the ip6.arpa zone instead of in-addr.arpa. The address is expanded to its full 32 hexadecimal digits. Each digit is then reversed and separated by dots to form the query domain. This tool handles the expansion and nibble formatting automatically, so just paste any IPv6 address.

Can one IP address have multiple PTR records?

Technically yes. The DNS standard allows multiple PTR records on one IP, and this tool displays every record it finds. In practice it is discouraged, especially for mail servers. Receiving systems may pick any of the hostnames when verifying the sender. Best practice is a single PTR record matching the server’s primary hostname.

Related tools and resources

Check out our other free networking tools. Look up forward DNS records for any domain or verify mail servers with an MX lookup. You can also find your own public IP address or explore IP binary conversion. You may also want to review DNS records explained for a deeper understanding of all record types including PTR.