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IP to Domain Lookup — Find Every Domain Hosted on an IP Address
Enter any IPv4 or IPv6 address and get a full list of domains that point to that IP via DNS records, or the canonical PTR hostname configured for it. One tool, two views: built for security analysts, sysadmins, and developers that need precise reverse-lookup data without juggling separate utilities.
Introduction
DNS works in two directions, and most people only think about one of them. The everyday direction, domain name to IP address, happens behind the scenes every time you open a website. The other direction, IP address to domain or hostname, is where things get interesting for anyone investigating, auditing, or operating a network.
The IP to Domain Lookup utility from APIFreaks combines two reverse-direction queries into a single tool. Enter an IP address, choose between Passrive Reverse DNS Lookup and DNS PTR Lookup, and you get two very different views of the same address.
Passive Reverse DNS Lookup returns every domain that has a DNS record pointing to the IP that is useful for shared-hosting analysis, threat intelligence, and infrastructure mapping. For a popular IP like 1.1.1.1, that can mean tens or even hundreds of thousands of associated domains. DNS PTR Lookup returns the single canonical hostname configured for that IP by its owner, the kind of record that mail servers, ISPs, and reverse-proxy operators rely on for identity and trust.
Whether you're tracing an attacker's infrastructure, debugging a mail delivery problem, or auditing the neighbourhood your website lives in, this one utility gives you both perspectives without forcing you to chase down separate tools.
What Would You Get From This Tool?
The tool returns one of two output sets, depending on which mode you toggle. You can switch between modes on the same IP to see both views in succession.
Mode 1: Passive Reverse DNS Lookup
Returns every domain currently associated with the queried IP address via DNS records. For a heavily shared or anycast IP, this list can be enormous. So, the tool also provides a precise total count and a paginated view of the first 100 records.
| Output Field | What It Tells You |
|---|---|
| Total Records | See the exact number of domains pointing to an IP at a glance — 181,655 for a shared host like 1.1.1.1, or just a handful for a dedicated server, instantly revealing server density. |
| Domain List | Browse a clean, paginated list of the first 100 domains resolving to the IP — no guesswork, no manual digging. Use total records to gauge full scope before diving in. |
| Last Seen | For every domain in the list, see the most recent date that DNS mapping was observed — helping you separate active relationships from stale, outdated ones. |
Mode 2: DNS PTR Lookup
Returns the canonical hostname configured for the IP address through its PTR (pointer) record. Unlike the reverse lookup above, a PTR record is a single, manually configured DNS entry set by the IP block owner, typically the hosting provider or ISP. There's usually only one.
| What You Get | Why It's Valuable |
|---|---|
| PTR Hostname | The official hostname assigned to the IP in its PTR record. For 1.1.1.1, this returns one.one.one.one, Cloudflare's canonical name for that IP. |
When to Use Which Mode
| What You Get | Why It's Valuable |
|---|---|
| Passive Reverse DNS Lookup | See every domain hosted on a server, map an attacker's infrastructure, audit shared hosting neighbours, or measure how widely an IP is used. |
| DNS PTR Lookup | Verify email sender reputation, debug forward-confirmed reverse DNS (FCrDNS), confirm a server's canonical name, or troubleshoot mail-delivery and trust issues. |
Why This Matters?
| What You Get | Why It's Valuable |
|---|---|
| Total Domains Count | Quickly assess server density. A server hosting 2,000 domains is a very different risk profile from one hosting 5. |
| Full Domains List | See every co-hosted site on a shared server in one place. No guesswork, no manual digging. |
| Real-time DNS Data | Results reflect current DNS records, not stale crawl data or search engine snapshots. |
How to Use the IP to Domain Lookup?
This is a subscriber-only utility. You'll need an active APIFreaks subscription and be Signed In before running a query
- Sign in to your APIFreaks account at apifreaks.com/login .
- Navigate to Utilities → IP to Domain Lookup or go directly to apifreaks.com/utilities/ip-to-domain-lookup .
- Use the output toggle to select either "Passive Reverse DNS Lookup" or "DNS PTR Lookup" depending on what you want to see.
- In the Enter IP Address field, enter the IP address you want to look up, for example 1.1.1.1.
- Click the Domain Lookup button. Within seconds, the tool returns the result for the selected mode.
- For Passive Reverse DNS Lookup, review the total domain count and scroll through the first 100 domains and their last-seen dates. For DNS PTR Lookup, see the canonical hostname returned for the IP.
- Toggle to the other mode if you'd like to see the alternative view of the same IP — no need to re-enter the address.
Tips for Best Results
- Use IPv4 addresses in dot-decimal notation (e.g., 8.8.8.8). Most public-facing servers are reachable this way.
- For Passive Reverse DNS Lookup on a CDN-shared IP (Cloudflare, Fastly, Akamai), expect very large counts as the IP is shared across many customers.
- For PTR Lookup, an absent or unhelpful result usually means the IP block owner hasn't configured a meaningful PTR record. This is itself a useful diagnostic signal as most legitimate mail servers should have one.
- If you're investigating a domain rather than an IP, run a forward DNS lookup first, take the resulting IP, and feed it back into this tool.
Use Cases
The dual-mode design opens a broader set of use cases than a single-mode reverse DNS lookup. Some scenarios call for the full domain list; others call for the canonical PTR hostname. Many require both.
Security Research & Threat Intelligence (Reverse mode)
When a suspicious IP appears in a firewall log or threat feed, the first step is mapping the infrastructure behind it. Reverse DNS Lookup reveals the full set of domains hosted on that IP, often surfacing co-located malicious sites, phishing kits, or command-and-control hostnames that share the same server.
Email Deliverability & Mail Server Trust (PTR mode)
Mail servers like Gmail, Microsoft 365, and Yahoo perform a PTR lookup on the sending IP of every inbound message. If the PTR record is missing, doesn't match the sender's HELO/EHLO banner, or doesn't resolve back to the same IP via a forward A record (a check known as Forward-Confirmed Reverse DNS), the message is likely to be filtered as spam or rejected outright. Use PTR Lookup to verify what major providers see when your server tries to deliver mail.
Shared Hosting Reputation Analysis (Reverse mode)
Search engines and email providers factor in the reputation of your hosting neighbourhood. If you're on shared hosting, the other websites on your server can affect your domain's deliverability, blacklisting risks, and search rankings. Use Reverse DNS Lookup to audit how many domains share your server IP and decide whether it's time to move to dedicated hosting.
Penetration Testing & Reconnaissance (Reverse mode)
During the reconnaissance phase of a sanctioned pentest, reverse IP address lookup is a standard technique for expanding the known attack surface of a target organization. A seemingly hardened primary domain may be co-hosted with a less secure sister site. Identifying all domains on an IP is a foundational step in building a full target profile.
Network Troubleshooting & SSH Banner Issues (PTR mode)
Slow SSH connections, broken syslog forwarding, and 'reverse DNS does not match SMTP banner' alerts often trace back to PTR misconfiguration. Use PTR Lookup to quickly diagnose whether the server's reverse DNS is set up correctly.
Domain & Server Migration Planning (Reverse mode)
Before changing the server's IPs or migrating to a new host, sysadmins need an authoritative list of every domain currently pointing to the old IP. Reverse DNS Lookup provides this list in one query, far faster than walking through DNS panels for every domain.
Brand Protection & Phishing Investigation (Reverse mode)
Phishing operations often cluster impersonation domains on shared infrastructure. Reverse Lookup on the IP behind one phishing site frequently uncovers the entire campaign's domain set, providing evidence for takedown requests and registrar abuse reports.
Digital Forensics & Legal Investigations (Reverse mode)
Legal and compliance teams investigating digital fraud, copyright infringement, or other cyber incidents often need to document the full set of domains associated with a specific IP. Reverse DNS Lookup provides a list of records for use in reports and legal proceedings.
Verifying Server Identity & FCrDNS (PTR & Reverse together)
Forward-Confirmed Reverse DNS (FCrDNS) is the gold standard for server identity: the PTR record points to a hostname, and that hostname's A record points back to the same IP. Use PTR Lookup to retrieve the hostname, then a separate forward DNS lookup to confirm round-trip consistency. Misalignment here breaks mail delivery, breaks logging tools, and signals a misconfigured server.
FAQs
Passive Reverse DNS Lookup scans DNS A records (for IPv4) and AAAA records (for IPv6) across many domains to find every hostname currently pointing to the queried IP, typically returning a list of dozens, hundreds, or even hundreds of thousands of domains. DNS PTR Lookup queries a single PTR record set by the IP block owner and returns one canonical hostname. The two answer, related but distinct, questions: 'which domains use this IP?' versus 'what does this IP officially identify itself as?'
This is normal for shared infrastructure. A single IP can host hundreds of small websites on shared hosting or be part of a CDN's anycast range that serves millions of customers. For 1.1.1.1, Cloudflare's public DNS resolver, the tool returns about 181,655 domain associations because that IP is referenced in DNS by an enormous number of services.
PTR records are designed to be one-to-one. The owner of an IP block configures a single PTR record per address that says 'this IP's official name is X.' For 1.1.1.1, Cloudflare set that name to one.one.one.one. Some IPs have no PTR record at all, in which case the tool returns an empty result.
A PTR (pointer) record is a DNS record type that maps an IP address back to a hostname. Where an A record answers 'what IP does this domain point to?', a PTR record answers 'what hostname does this IP point to?'. PTR records live in a special reverse-DNS zone and are only configurable by the owner of the IP block, usually the hosting provider or ISP.
"Reverse DNS" is the general process of resolving an IP address to a hostname. The specific mechanism it uses is the PTR record. So, in practice, "reverse DNS lookup" and "PTR lookup" refer to the same operation. APIFreaks labels this mode "DNS PTR Lookup" to make the underlying record type explicit.
In Passive Reverse DNS Lookup, the Last Seen date tells you when each domain-to-IP mapping was most recently observed. A recent date means the domain is still actively pointing at the IP. An older date suggests that the domain has likely moved on but is still in the historical record.
Yes. But the current version of this utility is optimized for IPv4 addresses (e.g., 192.168.1.1). IPv6 support may vary depending on the data set coverage. For best results, use a standard IPv4 address.
Yes, but interpret results accordingly. Passive Reverse DNS Lookup on a CDN-shared IP returns every domain routed through that CDN node, which can be a very large and noisy set. PTR Lookup on the same IP returns the CDN's canonical hostname (like one.one.one.one for Cloudflare's 1.1.1.1). To investigate the actual origin server, you'll need to identify the origin IP separately.
The IP to Domain Lookup is a premium utility available to active APIFreaks subscribers. You'll need to sign in to your account to run a query. If you don't have a subscription yet, visit APIFreaks Pricingto see available plans.
DNS PTR Lookup is queried in real time against live DNS. Reverse DNS Lookup uses a continuously updated index of DNS records. The 'Last Seen' field shows when each individual mapping was most recently confirmed.
Reverse DNS Lookup returns the first 100 records in the UI to keep the page fast and readable. The total count field shows you the full size of the result set. For programmatic or large-scale access, consider integrating the corresponding APIFreaks DNS API endpoint.
No. This tool takes an IP address as input. To go the other direction (domain to IP, forward DNS, MX, NS, TXT, and so on), use the APIFreaks DNS Lookup API or the Bulk DNS Lookup API.
Two ways to ask the same question, 'what's this IP?', produce two very different answers. Knowing how each works helps you choose the right one and interpret the results correctly.
Every time a domain owner sets up a website, they create DNS A and/or AAAA records that map their domain to the server's IP address. When many domains point to the same IP — which is the norm in shared hosting, CDN, or virtual hosting environments — they all create A records pointing at that single address. Passive Reverse DNS Lookup walks this forward-mapping data in reverse: it collects A records across the DNS landscape and groups them by IP, so when you query an IP, you get back the full set of domains whose A records currently land on it. This is why a popular CDN IP can return hundreds of thousands of associated domains.
PTR records live in a special DNS zone called in-addr.arpa (for IPv4) or ip6.arpa (for IPv6). When you perform a PTR lookup on 8.8.8.8, the DNS system reverses the address to 8.8.8.8.in-addr.arpa and asks the owner of that reverse zone — typically Google in this case — what hostname they've configured. The result is a single, authoritative answer set by the IP block owner. PTR records are the basis of reverse DNS and are used by mail servers, security systems, and logging tools to verify the identity of any IP they interact with.
It's perfectly normal for the PTR record on an IP to be unrelated to the domains that point to it via A or AAAA records. A shared host might have a PTR like 'mail.exampleisp.net' on an IP that also serves thousands of customer websites. The PTR identifies the IP's owner, and the reverse-lookup results identify what's running on it. Looking at both gives you a complete picture.
The strongest form of server identity is FCrDNS: the PTR record points to a hostname, and that hostname's A record points back to the same IP. Major mail providers require FCrDNS for clean inbox delivery. Use this tool's PTR mode to retrieve the hostname, then run a forward DNS lookup on that hostname to verify it returns the original IP. If both directions agree, FCrDNS is in place.
A reverse IP lookup shows current DNS mappings. It does not show you which of those domains is the "primary" site for that server, nor does it reveal historical domains that have since moved off the IP. It also cannot see through CDN proxy layers to the origin. For that kind of investigation, pair this tool with the APIFreaks DNS History API , which lets you see how a domain's IP mappings have changed over time.