Reverse DNS
Lookup.
Enter any IPv4 or IPv6 address to fetch its PTR record — the hostname its operator has mapped it to. We forward-confirm the answer (FCrDNS) so you can see whether the rDNS is honest, the way mail servers and SSH logs do.
Reverse DNS resolves an IP address back to a hostname using a PTR record in the in-addr.arpa (IPv4) or ip6.arpa (IPv6) zone. Unlike forward DNS, the IP's network owner controls the answer — not the hostname's owner. Mail servers, SSH login logs, and security tools all use PTR plus forward-confirmation (FCrDNS) to filter spoofed claims.
Last reviewed: May 2026
Forward DNS answers "what IP does example.com resolve to?"
Reverse DNS answers the opposite question — "what hostname does
this IP belong to?" — using a record type called PTR (pointer).
The lookup runs against a special hierarchy: in-addr.arpa for IPv4 and
ip6.arpa for IPv6. Your IP 8.8.8.8 becomes the query
8.8.8.8.in-addr.arpa — octets reversed — and the answer is the PTR record
published by Google for that zone: dns.google.
The crucial detail is who controls the answer. Forward DNS is published by whoever owns the hostname. Reverse DNS is published by whoever owns the IP block — your hosting provider, your ISP, or the cloud platform you run on. That asymmetry is the whole reason rDNS is interesting: it's an independent claim about an IP, made by a party with no incentive to lie on the hostname's behalf.
A PTR by itself isn't proof of anything — anyone who controls an IP block can point its rDNS at any hostname they like. Forward-confirmed reverse DNS (FCrDNS) closes that gap: take the PTR's hostname, do a forward (A/AAAA) lookup on it, and check that the result matches the original IP. If the round-trip lines up, the rDNS is honest. Mail servers, SSH login logs, and security tooling all rely on this check, which is why this tool runs it automatically on every lookup.
Email deliverability. Receiving mail servers reject (or aggressively
spam-folder) messages from IPs without a PTR record, or with a PTR that doesn't
forward-confirm. Generic-looking rDNS (203-0-113-45.cust.example-isp.net)
is treated as residential and often blocked outright. If you run an outbound mail
server, FCrDNS is the table-stakes deliverability check — along with
SPF, DKIM, and DMARC.
Logging and incident response. When SSH, web servers, or firewalls
log a connecting IP, they typically log the reverse-DNS hostname too. A meaningful PTR
(ec2-3-92-118-42.compute-1.amazonaws.com) immediately tells you the
provider; a missing or generic PTR is a small signal that something may be off.
Search engine crawlers (Googlebot, Bingbot, ClaudeBot) are all verified by FCrDNS —
the bot's claimed identity is only trusted if rDNS forward-confirms.
Network troubleshooting. A traceroute hop with a friendly PTR tells you which carrier you're traversing; a hop without one is opaque. Spam-filter false-positive investigations almost always involve checking rDNS first. Anything you'd want to learn about who owns an IP starts here, with WHOIS filling in the registration side.
Why does my IP have no PTR record?
Most residential and dynamically assigned IPs either carry a generic ISP-formatted PTR or none at all. PTR records have to be configured by whoever controls the reverse DNS zone for the IP block — usually the IP's network owner (your hosting provider or ISP), not the end user. If you run a server on a cloud platform, you can almost always set rDNS from the provider's control panel.
How do I set up reverse DNS for my server?
You don't set PTR records in your own DNS zone — the owner of the IP block does. Contact your hosting provider or ISP and ask them to point rDNS for your IP at a hostname you control. AWS, Linode, Hetzner, OVH, and most other cloud platforms expose this directly in their control panel. Once it's set, verify it forward-confirms (the hostname's A/AAAA record needs to point back at the same IP) — this tool will tell you.
What is forward-confirmed reverse DNS (FCrDNS)?
FCrDNS means the PTR record for an IP resolves to a hostname, and a forward (A or AAAA) lookup of that hostname returns the same IP. It's the basic sanity check used by mail servers, SSH login logging, web analytics, and search-engine bot verification to filter out IPs claiming hostnames they don't actually own. Setting rDNS without forward-confirming it is effectively meaningless.
What's the difference between IPv4 and IPv6 reverse DNS?
Both use PTR records, but the reverse zone is different. IPv4 reverses the four octets and appends .in-addr.arpa (so 8.8.8.8 becomes 8.8.8.8.in-addr.arpa). IPv6 expands the address to all 32 hexadecimal nibbles, reverses them, and appends .ip6.arpa. The query is otherwise identical, and this tool handles both formats automatically.