Regular (forward) DNS resolves a domain name to an IP address — e.g., "what is the IP for google.com?" Reverse DNS (rDNS) resolves an IP address to a hostname — e.g., "what hostname is assigned to 8.8.8.8?" They use completely different DNS zones: forward DNS uses your domain's zone (example.com), while reverse DNS uses the in-addr.arpa zone for IPv4 and ip6.arpa for IPv6. They are also controlled by different parties: you control forward DNS for your domain, but reverse DNS for an IP is controlled by whoever owns the IP block — your ISP or hosting provider. You cannot set PTR records at your domain registrar; you must contact your IP block owner.

Having no PTR record is very common and has several typical causes: (1) Most residential and mobile ISPs — including Jio in India — do not configure PTR records for residential IP ranges. This is normal for home broadband. (2) Your hosting provider requires you to configure PTR manually — many VPS and dedicated server providers leave it blank until you set it in their control panel. (3) The IP was recently allocated or reassigned and the PTR hasn't been configured yet. (4) Some IP blocks are not fully delegated in in-addr.arpa, making PTR queries impossible. For email servers, not having a PTR record is a serious problem — Gmail and many other providers reject email from IPs without PTR. For general internet use (web browsing, downloading), no PTR has zero impact.

PTR records are set by the organisation that owns your IP block — not your domain registrar. For cloud servers (AWS, DigitalOcean, Hetzner, Vultr): look in your provider's control panel for a "Reverse DNS" or "PTR record" setting, usually in the networking section of your instance. Enter the hostname you want (e.g. mail.yourdomain.com). For dedicated servers: usually configured through WHM, your host's control panel, or a support ticket. For home broadband (Jio, Airtel, BSNL): contact your ISP's business/commercial support — residential connections typically cannot have custom PTR records set. Before setting PTR, first create an A record for your desired hostname pointing to the same IP — many providers validate this before allowing PTR configuration.

FCrDNS (Forward-Confirmed reverse DNS) is a two-step check used by Gmail, Outlook, and many enterprise mail servers to verify that a sending IP's PTR hostname correctly points back to the same IP. Step 1: reverse DNS lookup on the connecting IP returns a hostname. Step 2: forward DNS lookup on that hostname must return the same original IP. If Step 2 fails or there is no PTR at all, Gmail returns a 550-5.7.25 error ("The IP address does not have a PTR record") and permanently rejects the email. This is one of the most common causes of new mail server setup failures. Both the PTR record AND a matching A record for the mail hostname are required for Gmail delivery.

The in-addr.arpa zone is the special DNS zone where PTR records for IPv4 addresses are stored. It works by reversing the octets of an IP address and appending .in-addr.arpa. For example, to look up the PTR for 8.8.8.8, a DNS resolver queries "8.8.8.8.in-addr.arpa" for a PTR record. The octets are reversed because DNS delegation works from right to left (most general to most specific), and reversing the IP makes it consistent with how domain zones are organised. IPv6 addresses use ip6.arpa in the same way but with each hexadecimal nibble reversed individually.

A PTR hostname can reveal several things about the IP depending on how the owner has configured it: (1) The owning organisation — "amazonaws.com" means AWS, "hetzner.com" means Hetzner, "airtel.net" means Airtel India. (2) The service type — "ec2" in an AWS PTR means an EC2 virtual machine; "broadband" in an ISP PTR means residential broadband. (3) The region or data centre — AWS PTR hostnames encode the region: "ap-south-1" means Mumbai, "us-east-1" means Northern Virginia. (4) The actual IP encoded in the hostname — many ISPs and hosts encode the IP digits in the PTR hostname for identification. (5) Whether it's a business or residential connection — "static", "server", "dedicated" suggest business lines; "dynamic", "broadband", "cable", "dsl" suggest residential.

Technically, the DNS specification allows multiple PTR records for a single IP address. However, in practice, most mail servers and network tools only process the first PTR record returned, and having multiple PTR records for a mail server IP is generally considered bad practice. RFC 1912 recommends that each IP should have exactly one PTR record, and that PTR should match exactly one A record (FCrDNS). For mail server IPs, configure exactly one PTR that matches exactly one A record pointing back to the same IP. Multiple PTR records on a single IP can cause unpredictable behaviour in mail server validation.

These are two entirely different tools that answer different questions: Reverse DNS Lookup (this page) performs a DNS PTR record query to find the hostname the IP block owner has configured for that specific IP address. It returns one hostname per IP. Reverse IP Lookup (our separate tool) queries web hosting databases to find all domain names that are currently hosted on a given IP address — it can return dozens or hundreds of websites sharing the same server IP. Reverse DNS uses the in-addr.arpa DNS zone; Reverse IP lookup uses web crawl data and hosting databases. Neither is a substitute for the other.

Google officially recommends this two-step reverse DNS verification to confirm a visitor is genuine Googlebot: (1) Run a reverse DNS lookup on the IP claiming to be Googlebot — the PTR hostname must end in .googlebot.com or .google.com. (2) Run a forward DNS lookup on that hostname — it must resolve back to the original IP. If both steps pass, the visitor is confirmed genuine Googlebot. Command-line method: dig -x [IP] +short to get hostname, then dig [hostname] A +short to verify it returns the same IP. This verification is important because anyone can set their HTTP User-Agent to "Googlebot" — only genuine Google crawlers have the matching PTR records in Google's managed DNS zones.

Yes — completely free, unlimited lookups, no account or signup required. The tool performs a live DNS PTR query via Google DNS-over-HTTPS, returning the real-time PTR record for any public IPv4 or IPv6 address. It also performs a forward FCrDNS verification check and fetches ISP, ASN, and geolocation data for additional context. We do not store or log the IP addresses you look up.