What is Reverse IP Lookup?

Reverse IP Lookup is the process of taking an IP address and finding out which domains are hosted on that IP. It’s the reverse of DNS lookup, where you start with a domain and retrieve its IP address.

How Does Reverse IP Lookup Work?

Here’s a breakdown of how it works under the hood:

1. Querying PTR Records: Sometimes, the reverse DNS record (PTR) will directly map an IP to a domain.

2. Scanning Hosting Data: Public databases and passive DNS records are used to check which domains have pointed to the IP.

3. Web Crawling: Tools crawl IP-hosted servers and check for HTTP headers, certificates, or server response metadata.

4. Aggregated Hosting Data: Some services use real-time hosting snapshots or WHOIS data to map domains to IPs.

Reverse IP Lookup isn’t just about technical curiosity—it’s a valuable method for uncovering relationships between domains sharing the same host. By identifying additional hostnames associated with an IP, you can gain deeper insight into the infrastructure behind a target domain. These new hostnames may reveal further DNS records, offer clues about the organization’s other assets, or even expand the scope for cybersecurity testing and analysis. Even if no immediate vulnerabilities are discovered, the technique enriches your overall information discovery process, equipping you with a broader perspective for investigations, audits, or competitor research.

It’s important to note that reverse IP lookup and reverse DNS lookup are related but distinct processes.

In a reverse DNS lookup, the IP address is checked against a DNS server to see if there’s a pointer (PTR) record assigned by the owner of the IP address block. This record, if present, reveals the canonical domain name for that IP. However, a PTR record typically points to just one domain—even if the IP hosts many domains.

Reverse IP lookup, on the other hand, pulls from multiple sources—such as passive DNS, public hosting data, and web crawling—to compile a list of all domains hosted on the IP, not just the one assigned in the PTR record. This broader approach is what makes reverse IP lookup so useful for uncovering shared hosting environments, mapping infrastructure, or identifying potentially related websites.

What is CIDR Search and How Does It Enhance Reverse IP Lookup?

CIDR (Classless Inter-Domain Routing) search expands the Reverse IP Lookup function by letting you investigate not just a single IP, but an entire block of addresses—often up to a /24 network (256 addresses). Instead of searching for domains on one IP, you can uncover all domains hosted across a whole subnet. This is useful when:

• Researching infrastructure used by an organization or competitor

• Analyzing shared hosting providers or cloud resource allocations

• Mapping server neighbors that might affect your own site’s performance or reputation

To use CIDR search, simply input an IP range (like 203.0.113.0/24). The lookup tool scans all the IPs in that range to list every domain it finds, giving you broader visibility than checking a single address. This can help you track down related sites, spot bad actors using multiple nearby IPs, or better understand the hosting landscape.

Using Bing for Reverse IP Searches

Bing offers a handy feature for reverse IP lookups. If you're curious which domains are hosted on a specific IP address, you can use Bing’s search operators to dig up the information directly from its index. Simply type ip:YOUR.IP.ADDRESS into the Bing search bar, swapping in the IP address you're interested in.

For example:
ip:192.185.30.10

When you run this query, Bing will list websites it knows are operating from that IP. This approach is especially useful for uncovering shared hosting relationships, exploring adjacent domains for research, or conducting preliminary security checks. While results may not capture every single domain—especially for recently moved sites or those behind CDNs—the method is quick and requires no special tools or accounts.

This technique can supplement your reverse IP investigations, especially when paired with other lookup services for more comprehensive results.

Reverse IP Lookup: User Limits and Result Caps

Before you dive in, it’s helpful to know about usage limits depending on your access level. Free users can run up to 20 queries a day, with each search returning a maximum of 500 domains. This should be more than enough for smaller audits or quick spot checks.

If you need to cast a wider net—say, you’re a security analyst, penetration tester, or SEO professional digging into large datasets—membership unlocks much more generous allowances. Depending on your plan, members can perform hundreds (up to 20,000) of queries per day, and retrieve results for hundreds of thousands, even up to 10 million domains per search when using the API.

In short:

• Free users: 20 queries per day, up to 500 results per search.

• Members: Up to 20,000 queries daily, and up to 10 million domains per query via API.

Most users will find the free tier sufficient for casual investigations or technical due diligence. If your workflow requires deep-dive bulk queries—especially for research or enterprise purposes—consider upgrading to unlock full access.

Practical Examples

Example 1: Finding All Sites on a Shared Host

Input:

IP: 192.185.30.10

Output:

- example-blog.com  
- myshopstore.net  
- vintagecars.org

Useful for: Competitor analysis or discovering clients hosted on a shared server.

Reverse IP Lookup is especially valuable in environments where a single IP address hosts multiple virtual hosts—a standard practice in shared hosting and within many organizations. By identifying all domains associated with an IP, you can uncover other websites that might be less secure or poorly maintained. For example, if your primary target site appears locked down, you might discover a forgotten blog or outdated client portal on the same server. These additional domains can expand your view of the server’s attack surface and potentially reveal easier entry points for further investigation or remediation.

This approach isn’t just for cybersecurity—it's also a favorite for SEO professionals analyzing who shares their hosting environment, or for businesses conducting competitive intelligence. Whether you’re tracking down rival e-commerce stores or checking for neighbors in a cloud setup, Reverse IP Lookup provides an invaluable map of who’s living at a given digital address.

Example 2: Security Audit

You’re investigating a suspicious IP used in phishing emails. Using reverse lookup, you find other domains on that IP, some of which are also flagged.

Reverse IP Lookup: Expanding the Investigation

Reverse IP lookup is a technique for identifying hostnames (or domains) associated with a particular IP address via DNS records. This becomes particularly useful because web servers often host multiple virtual domains on a single IP—think of shared hosting providers or organizations consolidating resources.

This means that if your primary target domain appears locked down, there may be other, less secure sites sharing that same IP. Attackers often exploit these secondary domains to slip past robust defenses, so discovering them can significantly widen your view of the threat landscape.

Use Case: Helps in threat intelligence and IP reputation checks.

By identifying all domains sharing an IP, you can spot related malicious activity, detect compromised sites on the same server, and prioritize domains for further investigation.

Accessing Reverse IP Lookup via API

If you prefer automation or want to integrate reverse IP lookups directly into your workflow, you can use our straightforward API. Fetch hosted domains tied to a specific IP address using simple HTTP requests—compatible with curl, Python, or just about any tool that makes web requests.

Quick Start Example

To get started, craft a request like this:

You’ll receive a plain text listing of domains associated with the IP address.

Pagination and Large Result Sets

For IPs with a massive number of hosted domains, the API supports pagination. Just add a &page= parameter to your query to fetch additional result pages—up to 10 million results (20 pages) per IP for higher membership tiers.

Usage Limits

• Free users: 50 queries per day, up to 500 results per query.

• Full Members: Higher quotas available, allowing for larger datasets and increased daily limits.

This design keeps things speedy and simple, so you can focus on analyzing your data rather than wrestling with integration.

Retrieving Larger Result Sets with Pagination

Need results beyond the standard response limit? Most reverse IP lookup APIs support pagination, allowing you to access much larger datasets—sometimes up to 10 million records per IP. Simply include a page parameter (often &page= or similar) in your API request to move through the results in batches. For example, specifying different page numbers will let you step through multiple sets of domains associated with the same IP.

This approach is ideal for extensive analysis or when you’re working with high-traffic IPs that host a vast number of domains. Just check your API provider's documentation for the exact parameter syntax and any usage limits that may apply to your membership level.

Use Cases

• SEO: Identify if your site shares an IP with spammy or blacklisted domains

• Cybersecurity: Detect phishing, malware distribution, or malicious hosting clusters

• Hosting Insights: Evaluate server sharing in budget hosting or cloud setups

• Network Troubleshooting: Trace routing conflicts or misconfigured reverse DNS entries

Reverse IP lookup is also valuable for:

• Network enumeration: Mapping organizational assets for IT governance.

• Reconnaissance: Preparing for penetration testing by discovering interlinked domains and potential attack surfaces.

A reverse IP lookup isn’t just about technical curiosity—it’s a practical tool for assessing your web host’s reputation. By revealing which other websites share your server, you can uncover potential risks to your own domain. If your neighbors include spam or phishing sites, this could lead to blacklisting, poor email deliverability, or even a negative impact on your search engine rankings.

Consider using investigative tools to vet these co-hosted domains. Spotting a pattern of low-quality or malicious sites on your host can be a red flag—one that’s worth addressing before it affects your online presence.

Practical Applications of Reverse IP Lookup

Reverse IP lookup serves as a Swiss Army knife for anyone interested in understanding more about an IP address and its associated domains. Here’s how it’s commonly put to work:

Attack Surface Discovery

Security teams—whether defending or probing—often use reverse IP lookups to map out the visible “attack surface” of a host. By uncovering the full roster of domains sharing an IP, they can identify unexpected web applications or forgotten subdomains, exposing weak points that might otherwise fly under the radar. Even if vulnerabilities aren’t immediately apparent, simply discovering additional hostnames can expand the information discovery cycle, leading to new avenues for investigation.

Incident Response & Threat Intelligence

During incident response, reverse IP lookup helps track down hostnames tied to suspicious or malicious activity, such as phishing operations, malware distribution, or command-and-control servers. By correlating domains with an offending IP, analysts can piece together a broader view of the threat landscape and identify further indicators of compromise.

Shared Hosting and Oversubscription

In shared hosting environments—think GoDaddy, Bluehost, or any budget provider—it’s not uncommon for a single server to host hundreds or even thousands of websites. This can lead to oversubscription, where too many sites compete for limited resources. Using reverse IP lookup, you can see just how crowded your digital neighborhood is, providing useful context on performance and security considerations.

Web Reputation and Blacklisting

A server’s reputation can affect not just one site, but all sites sharing its IP. If your neighbors engage in spam or shady activity, you might find your own emails blocked or your site’s SEO taking a hit. Regularly checking who you’re sharing space with can help you catch reputation risks early and take action before search engines or spam filters do.

Reverse IP lookup is more than just a technical curiosity—it’s a practical tool for site owners, security professionals, and anyone wanting a clearer picture of their online environment.

Pro Tips

• Combine with DNS tools like DNS Lookup to map the full domain infrastructure.

• Use IP Address Validator to confirm your input IP is properly formatted before lookup.

• Check ownership: Use WHOIS tools in tandem to verify domain ownership or registrant details.

• For deeper insights, supplement with vulnerability scans and passive DNS search to detect historical domain-IP associations or exposed services.

• Always ensure your recon remains ethical and within legal boundaries

• Reverse IP lookups may not work on CDN-backed sites like Cloudflare; use direct origin IP when possible.

• Shared hosting can reveal dozens of unrelated domains—filter results by country or name server for relevance.