Reverse DNS Lookup
Find the hostname associated with an IP address by looking up its PTR record, with forward verification to confirm the mapping.
What is Reverse DNS?
Reverse DNS (rDNS) is the process of resolving an IP address back to its associated hostname. This is done by looking up the IP's PTR (pointer) record in the DNS system.
Unlike regular DNS which maps hostnames to IPs, reverse DNS maps IPs to hostnames. This is useful for verifying server identity, email authentication, and network troubleshooting.
Why PTR Records Matter
- Email servers check PTR records to verify sender identity
- Missing PTR records can cause email delivery problems
- Security tools use rDNS to identify malicious hosts
- Network administrators use it for logging and monitoring
- Some services require valid rDNS before allowing connections
How Reverse DNS Works
IP Reversal
The IP address is reversed and appended to in-addr.arpa (IPv4) or ip6.arpa (IPv6). For example: 8.8.8.8 becomes 8.8.8.8.in-addr.arpa
PTR Lookup
DNS servers are queried for the PTR record at that address. The PTR record contains the hostname associated with the IP.
Forward Verification
We verify the hostname by checking if it resolves back to the original IP. This confirms the PTR record is legitimately configured.
Frequently Asked Questions
Why does my IP have no PTR record?
PTR records must be set up by whoever controls the IP address, usually your ISP or hosting provider. Many residential ISPs don't configure PTR records for customer IPs, which is normal for home connections.
What does "Forward verification failed" mean?
This means the hostname in the PTR record doesn't resolve back to the original IP address. This could indicate a misconfigured DNS or that the PTR record is outdated. Properly configured reverse DNS should always verify.
How do I set up a PTR record for my IP?
Contact your ISP or hosting provider. They control the reverse DNS zone for their IP ranges. For cloud providers like AWS or Google Cloud, you can usually configure PTR records through their management console.
Does reverse DNS work with IPv6?
Yes! IPv6 reverse DNS works the same way but uses the ip6.arpa domain instead of in-addr.arpa. The process is identical - enter any IPv6 address and we'll look up its PTR record.