Reverse DNS Lookup Tool
Understanding Reverse DNS & PTR Records
A guide to how reverse DNS works, what PTR records are, who controls them, and how to interpret lookup results.
What Is Reverse DNS?
Standard (forward) DNS translates a hostname into an IP address — for example, resolving google.com to 142.250.80.46. Reverse DNS does the opposite: it maps an IP address back to a hostname.
This mapping is stored in a special DNS record type called a PTR record (Pointer record). When you query the reverse DNS for 8.8.8.8, the answer is dns.google — the hostname Google has registered for that IP.
Unlike forward DNS — where anyone who controls a domain can create records — PTR records can only be set by the organisation that has been allocated the IP address block by its Regional Internet Registry (RIR). In practice, this means your ISP or hosting provider controls the PTR record for any IP they assign to you.
ℹ PTR records are optional
How PTR Records Work
To make reverse lookups work within the existing DNS infrastructure, IP addresses are stored as hostnames in special reserved zones. The lookup process follows the same hierarchy as any other DNS query.
2.1 — The in-addr.arpa Zone (IPv4)
IPv4 reverse DNS uses a special zone called in-addr.arpa. To look up the PTR record for an IP address, the octets are reversed and .in-addr.arpa is appended. This reversed format lets the DNS hierarchy delegate zones by the most significant octet first — matching how IP blocks are allocated.
| IP Address | PTR Query Name |
|---|---|
| 8.8.8.8 | 8.8.8.8.in-addr.arpa |
| 1.1.1.1 | 1.1.1.1.in-addr.arpa |
| 9.9.9.9 | 9.9.9.9.in-addr.arpa |
| 192.168.1.100 | 100.1.168.192.in-addr.arpa |
The tool handles this conversion automatically — you just enter the IP address and the correct query format is constructed for you.
2.2 — IPv6 Reverse DNS
IPv6 reverse DNS works the same way but uses the ip6.arpa zone instead. Each hexadecimal nibble of the fully expanded IPv6 address is reversed individually and separated by dots.
Example — Cloudflare DNS IPv6
ℹ IPv6 PTR records are rarer
Forward vs Reverse DNS
Forward and reverse DNS are independent systems — they don't automatically stay in sync with each other. A PTR record pointing to a hostname doesn't mean that hostname's A record points back to the same IP.
| Forward DNS | Reverse DNS | |
|---|---|---|
| Direction | Hostname → IP address | IP address → hostname |
| Record type | A (IPv4) / AAAA (IPv6) | PTR |
| Zone | Your domain zone (e.g. example.com) | in-addr.arpa / ip6.arpa |
| Controlled by | Domain owner | IP block owner (ISP / hosting provider) |
| Required | Yes — without it the domain is unreachable | No — optional but important for email and logging |
✉ Forward-confirmed Reverse DNS (FCrDNS)
Who Sets PTR Records?
PTR records are controlled by whoever owns the IP address block — not the domain owner. This is a fundamental difference from forward DNS.
ISP (broadband customers)
Your ISP owns the IP block assigned to home and business connections. They set generic PTR records like customer-123-45-67-89.isp.net. You typically cannot customise this without a business account or static IP arrangement.
Hosting provider / VPS
Cloud and dedicated server providers (AWS, DigitalOcean, Hetzner, etc.) allow you to set a custom PTR record for your server's IP via their control panel or API. This is essential for running a mail server.
Enterprise (own IP allocation)
Organisations that hold their own ARIN/RIPE allocation control the reverse DNS zone entirely and can set PTR records for any IP in their block.
Cloud providers (shared IP)
On shared infrastructure where you don't have a dedicated IP (e.g. shared hosting), the provider sets the PTR and you typically cannot change it.
How to Use This Tool
The tool accepts any public IPv4 or IPv6 address and returns the PTR record registered for it.
Enter an IP address
Type any IPv4 (e.g. 8.8.8.8) or IPv6 (e.g. 2606:4700:4700::1111) address. The tool automatically constructs the correct in-addr.arpa or ip6.arpa query.
Click Lookup
The PTR record is fetched from public DNS and returned within 1–2 seconds.
Use example IPs
Click any of the example IP buttons below the form to pre-fill well-known addresses and see how PTR records look for major providers.
💡 Tip — Well-known PTR examples
Interpreting Results
The result shows the PTR hostname registered for the queried IP. There are three possible outcomes:
PTR record found
A hostname is returned. This is the name the IP block owner has registered. It may be a meaningful name (mail.company.com) or a generic template (customer-x-x-x-x.isp.net).
Multiple PTR records
Some IPs have more than one PTR record — though this is unusual and generally considered a misconfiguration. The tool shows all records when multiple exist. For email purposes, only the first is typically used.
No PTR record (NXDOMAIN)
The IP exists and is routable but no PTR record has been configured. Common for residential broadband IPs, private address space, and poorly maintained infrastructure. Not necessarily an error — just means reverse DNS wasn't set up.
Reading PTR hostnames from common providers:
| PTR Hostname Pattern | What It Indicates |
|---|---|
| ec2-x-x-x-x.region.compute.amazonaws.com | Amazon AWS EC2 instance |
| x.x.x.x.bc.googleusercontent.com | Google Cloud Compute Engine |
| x-x-x-x.lightspeed.isp.sbcglobal.net | AT&T residential broadband |
| mail.company.com | Custom PTR — likely a mail server |
| tor-exit.hostname.example | Tor exit node (common naming convention) |
| scanner.shodan.io / probe.example.com | Security scanner or research network |
Practical Use Cases
Reverse DNS is a foundational tool for anyone working with network infrastructure, email, or security.
Email deliverability
Mail servers check PTR records before accepting email. If your mail server's IP has no PTR record, or the PTR doesn't match the forward A record, messages are likely to be rejected or marked as spam.
Identify server ownership
PTR records often reveal who operates a server — ISP, cloud provider, CDN, or a specific company. A hostname like mail.company.com or cdn.cloudflare.com is immediately recognisable.
Network troubleshooting
In MTR and traceroute output, hops that resolve to hostnames are far easier to interpret than raw IPs. PTR records turn 192.0.2.1 into core1.ny.isp.net, revealing the network and location.
Security investigation
Suspicious IPs hitting your infrastructure can be investigated via PTR — a hostname like scanner.shodan.io or tor-exit.example.com gives immediate context about the traffic source.
Verify your own server
After configuring PTR records for a mail or web server, use this tool to confirm the record is live and resolving correctly from public DNS.
Identify cloud & CDN IPs
Cloud providers use structured PTR naming conventions. AWS IPs resolve to ec2-x-x-x-x.region.compute.amazonaws.com; Cloudflare IPs resolve to predictable hostnames — useful for confirming traffic paths.