Reverse DNS Lookup

Find the hostname associated with any IPv4 or IPv6 address via PTR record lookup

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Frequently Asked Questions

Reverse DNS (rDNS) is the process of resolving an IP address back to a hostname. While standard DNS lookup resolves a domain name to an IP address (forward lookup), reverse DNS does the opposite — it queries a PTR (Pointer) record in the special in-addr.arpa domain (for IPv4) or ip6.arpa (for IPv6) to find the associated hostname.

A PTR (Pointer) record maps an IP address to a domain name. PTR records are stored in the reverse DNS zone and are used by mail servers to verify the identity of sending servers, network diagnostics, and system logging. For example, the IP 8.8.8.8 resolves to dns.google via a PTR record.

Not all IP addresses have PTR records configured. PTR records must be set up by the IP block owner (typically an ISP or hosting provider). Consumer IP addresses often don't have PTR records. Servers and mail servers usually do — mail servers without valid reverse DNS are often flagged as spam.

Forward-confirmed reverse DNS (FCrDNS) is when the hostname resolved via PTR record also resolves back to the same IP via an A record. For example: 8.8.8.8 → dns.google → 8.8.8.8. This confirmation is used by email servers to verify that a server's IP and hostname are consistent, which is a strong spam prevention signal.

Email servers often check the reverse DNS of the connecting server's IP. If the PTR record doesn't exist or doesn't match the sending domain, the email is more likely to be flagged as spam. For email deliverability, it's important that your mail server's IP has a PTR record pointing to a hostname that resolves back to that same IP (FCrDNS).

Yes. This tool supports both IPv4 and IPv6 reverse DNS lookups. For IPv6, the lookup queries the ip6.arpa zone instead of in-addr.arpa. For example, the IPv6 address 2001:4860:4860::8888 (one of Google's DNS servers) resolves to dns.google. IPv6 PTR records are less commonly configured than IPv4 ones.

An A record performs forward DNS resolution — it maps a hostname to an IP address (e.g. mail.example.com → 203.0.113.10). A PTR record performs reverse DNS resolution — it maps an IP address back to a hostname (e.g. 203.0.113.10 → mail.example.com). PTR records are stored in the special in-addr.arpa zone and are managed by the IP block owner (usually your ISP or hosting provider), not your domain registrar. Both records must agree for forward-confirmed reverse DNS (FCrDNS), which is important for mail server trust.

Many mail servers perform a reverse DNS check on the IP of any connecting server. If your mail server's IP has no PTR record, or the PTR record does not match the server's hostname, the receiving mail server may reject the email outright or assign it a high spam score. Major providers like Gmail, Outlook/Hotmail, and Yahoo Mail all factor reverse DNS into their deliverability decisions. Having a valid PTR record that matches your SMTP hostname (and that hostname resolving back to the same IP via an A record) is one of the baseline requirements for reliable email delivery.

Unlike A and CNAME records, PTR records are controlled by the owner of the IP block — not by your domain registrar. To set up a PTR record, contact your ISP or hosting provider (e.g. DigitalOcean, Hetzner, AWS, Linode). Most cloud providers offer a self-service option in their control panel under server or network settings (look for "Reverse DNS" or "PTR Record"). Set the PTR value to your mail server's fully qualified domain name (FQDN), then create a matching A record in your DNS zone. After setting up, use this tool to verify the PTR record is propagating correctly.

For IPv6, reverse DNS uses the ip6.arpa domain with a nibble format: the full 128-bit address is expanded to 32 hex digits, reversed nibble by nibble, and each digit separated by dots. For example, the address 2001:db8::1 expanded is 20010db8000000000000000000000001, and its PTR query becomes 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. IPv6 PTR records are less commonly set than IPv4 — even many server operators skip them — but they are equally important for mail deliverability if you send email over IPv6.

About This Reverse DNS Lookup Tool

This free Reverse DNS (rDNS) Lookup tool performs a PTR record lookup for any public IPv4 or IPv6 address. It also attempts a forward confirmation lookup — verifying that the resolved hostname maps back to the original IP. Private, loopback, and reserved IP addresses are blocked for security.

Well-known DNS Server IPs

IP	Provider	Hostname
8.8.8.8	Google	dns.google
1.1.1.1	Cloudflare	one.one.one.one
9.9.9.9	Quad9	dns9.quad9.net
208.67.222.222	OpenDNS	resolver1.opendns.com
4.2.2.2	Level3	b.resolvers.Level3.net

Reverse DNS Use Cases

Use Case	Why it Matters
Email deliverability	PTR required by many mail servers
Network diagnostics	traceroute/ping show hostnames
Security logging	Logs show hostnames not just IPs
Spam prevention	FCrDNS check by mail servers
Abuse investigation	Identify servers behind an IP

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