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Reverse DNS Lookup

Perform a reverse DNS lookup (PTR record query) to find the hostname associated with any IP address.

About Reverse DNS Lookup

The Reverse DNS Lookup tool performs PTR record queries to find the hostname(s) associated with an IP address — the opposite direction of a normal DNS lookup which resolves hostname to IP. Reverse DNS is used in email deliverability (mail servers verify that the sending IP has a matching PTR record), network diagnostics, security auditing, and identifying server operators from IP addresses found in access logs. The tool supports both IPv4 and IPv6 reverse DNS lookups using the in-addr.arpa and ip6.arpa domains respectively. Multiple PTR records for a single IP are all returned.

Why use Reverse DNS Lookup

  • Supports both IPv4 (/in-addr.arpa/) and IPv6 (/ip6.arpa/) PTR lookups.
  • Returns all PTR records when multiple hostnames map to the same IP.
  • Useful for email deliverability diagnosis and server identification.
  • Browser-based tool with no installation required.
  • Supports both IPv4 (in-addr.arpa) and IPv6 (ip6.arpa) PTR lookups in one interface.
  • Returns all PTR records when multiple hostnames map to the same IP address.

How to use Reverse DNS Lookup

  1. Enter an IPv4 or IPv6 address in the input field.
  2. Click Lookup to retrieve the PTR record(s) for that IP.
  3. Review the returned hostname(s) associated with the IP.
  4. Use the result to identify the server operator or ISP.
  5. Click Lookup to query the appropriate reverse DNS zone (in-addr.arpa for IPv4, ip6.arpa for IPv6).
  6. Review the returned hostname(s) — most IPs have a single PTR record but some have multiple.
  7. Check the forward-confirmed status — the tool resolves the hostname back to an IP to verify FCrDNS.

When to use Reverse DNS Lookup

  • Verifying an email server's PTR record matches its A record (forward-confirmed rDNS).
  • Identifying the hostname of an IP address found in access logs.
  • Diagnosing email delivery failures caused by missing PTR records.
  • Security investigations to identify the operator of a suspicious IP.
  • Verifying an email server's PTR record matches its A record (Forward-Confirmed reverse DNS).
  • Identifying the hostname of an IP address found in web server access logs.

Examples

Public web server IP

Input: 93.184.216.34

Output: Reverse zone: 34.216.184.93.in-addr.arpa PTR: example.com Forward check: example.com → 93.184.216.34 ✓ FCrDNS passed TTL: 86400s

Google DNS resolver

Input: 8.8.8.8

Output: Reverse zone: 8.8.8.8.in-addr.arpa PTR: dns.google Forward check: dns.google → 8.8.8.8, 8.8.4.4 ✓ FCrDNS passed TTL: 21599s

IPv6 lookup

Input: 2606:2800:220:1:248:1893:25c8:1946

Output: Reverse zone: 6.4.9.1.8.c.5.2.3.9.8.1.8.4.2.0.1.0.0.0.0.2.2.0.0.0.8.2.6.0.6.2.ip6.arpa PTR: example.com TTL: 21600s

Tips

  • Always set rDNS for outbound mail servers — Gmail, Outlook, and Yahoo will reject mail from IPs without PTR records.
  • Set the PTR to match the HELO/EHLO hostname exactly for the strongest sender reputation signal.
  • FCrDNS verification means PTR → hostname AND hostname A record → original IP both must succeed — partial setup fails strict mail servers.
  • Cloud providers (AWS EC2, GCP, Azure) require you to manually request a custom PTR record — defaults look like ec2-1-2-3-4.compute-1.amazonaws.com.
  • If the PTR is missing on a critical IP, contact your hosting provider's support — most allow custom rDNS for free.
  • When debugging mail issues, also check IP reputation (Spamhaus, SURBL) — rDNS alone is not enough for inbox placement.
  • Multiple PTR records on one IP are technically allowed but often cause issues — most operators stick to one PTR per IP.

Frequently Asked Questions

Why does a reverse lookup return no results?▾
Not all IP addresses have PTR records configured. ISPs and hosting providers must explicitly set up reverse DNS for their IP ranges. Many residential IPs and cloud VM IPs do not have PTR records.
What is a FCrDNS check?▾
Forward-Confirmed reverse DNS (FCrDNS) requires that the PTR record points to a hostname whose A record resolves back to the original IP. Email servers use this check to identify legitimate mail senders.
How is a reverse DNS lookup structured?▾
For IPv4 (e.g. 93.184.216.34), the octets are reversed and appended to in-addr.arpa: 34.216.184.93.in-addr.arpa. A PTR query on this name returns the hostname.
Does it work for private IP addresses?▾
Private IP ranges (192.168.x.x, 10.x.x.x) can have PTR records on internal DNS servers, but they are not accessible from the public internet. This tool queries public DNS resolvers.
What does the PTR record contain?▾
A PTR record contains a domain name — typically the fully qualified hostname of the server at that IP address.
What is an FCrDNS check?▾
Forward-Confirmed reverse DNS requires that the PTR record points to a hostname whose A record resolves back to the original IP. Email servers like Gmail and Outlook use FCrDNS to verify that the sending IP belongs to the claimed hostname.

Explore the category

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Glossary

PTR record
Pointer record — a DNS record type that maps an IP address to a hostname. The reverse of an A or AAAA record. Stored in special reverse zones.
in-addr.arpa
The special DNS domain used for IPv4 reverse lookups. The IP's octets are reversed and appended (e.g. 93.184.216.34 → 34.216.184.93.in-addr.arpa).
ip6.arpa
The special DNS domain used for IPv6 reverse lookups. Each hex nibble of the IPv6 address is reversed and dot-separated under ip6.arpa.
FCrDNS
Forward-Confirmed reverse DNS — a verification method where the PTR hostname must resolve back to the original IP via an A/AAAA record. Required by most strict mail servers.
HELO/EHLO
The SMTP commands a mail client uses to identify itself to a mail server. Best practice: HELO hostname should match the PTR record on the sending IP.
SMTP banner
The greeting an SMTP server sends on connection (e.g. '220 mail.example.com ESMTP'). Some receivers compare the banner hostname to the PTR for additional verification.
Reverse zone delegation
The process where an ISP delegates control of an in-addr.arpa or ip6.arpa subzone to a customer so the customer can manage their own PTR records.
Authoritative answer
A DNS response from the server that holds the original record — as opposed to a cached response from a recursive resolver. The 'aa' flag in DNS messages.