Understanding Reverse IP Lookup
A reverse IP lookup is a technique that identifies all domain names hosted on a given IP address. While a standard DNS lookup translates a domain name into an IP address (forward resolution), a reverse IP lookup works in the opposite direction: given an IP address, it reveals every domain that resolves to it. This is an essential capability for security professionals, system administrators, and anyone investigating the infrastructure behind a website.
At reverseips.com, we make this process simple. Enter any IPv4 or IPv6 address and instantly see every domain our passive DNS database has observed pointing to that IP. Try it now with one of our example lookups on the homepage.
Why Do Multiple Domains Share the Same IP?
In the early days of the internet, each website typically had its own dedicated IP address. Today, it is extremely common for hundreds or even thousands of domains to share a single IP. This happens for several reasons:
- Shared hosting – Web hosting providers place many customer websites on the same server. The web server uses the HTTP Host header (or SNI for HTTPS) to route each request to the correct website, so a single IP can serve unlimited domains.
- Content Delivery Networks (CDNs) – Services like Cloudflare, Akamai, and AWS CloudFront proxy traffic through their own IP ranges. A single Cloudflare IP, for example, might front thousands of unrelated websites.
- Cloud providers – Platforms such as AWS, Google Cloud, and Azure host millions of sites behind load balancers that share IP pools. A reverse IP lookup can reveal which services coexist on the same infrastructure.
- Virtual Private Servers (VPS) – Budget VPS providers often assign the same IP to multiple customers using NAT or shared hosting configurations.
Use Cases for Reverse IP Lookup
Reverse IP lookups are a critical tool in many professional workflows:
- Security audits and penetration testing – Discovering all domains on a target IP helps identify the full attack surface. If one site on a shared server is compromised, others may be at risk. Security teams use reverse IP data to enumerate virtual hosts and find forgotten or shadow IT applications.
- Open-Source Intelligence (OSINT) – Investigators and journalists use reverse IP to map organizational infrastructure, uncover hidden relationships between domains, and trace the hosting footprint of threat actors.
- Competitive analysis – Marketers and business analysts can discover what other sites a competitor hosts on the same server, potentially revealing staging environments, test domains, or related brands.
- Abuse investigation – Hosting providers and abuse teams identify all domains on an IP to assess whether a server is involved in phishing, malware distribution, or spam campaigns.
How reverseips.com Works
Our tool queries the Profundis.io passive DNS intelligence API. Profundis continuously collects DNS resolution data from distributed sensors around the world, building a massive database of which domains point to which IP addresses over time. When you perform a reverse IP lookup on reverseips.com, we search this database for all A and AAAA records whose value matches your query.
The free tier on reverseips.com shows a generous number of results. For unlimited access, full historical data, and API integration, visit Profundis.io.
Forward DNS vs. Reverse DNS: What is the Difference?
These terms are often confused, but they refer to distinct concepts:
- Forward DNS lookup – Translates a domain name to an IP address (e.g., example.com → 93.184.216.34). This is what your browser does every time you visit a website.
- Reverse DNS lookup (PTR) – Translates an IP address back to a hostname using PTR records in the in-addr.arpa zone. This is configured by the IP owner and typically returns a single canonical hostname for the server, not every domain hosted on it.
- Reverse IP lookup (passive DNS) – What reverseips.com does. It searches observed DNS resolution data to find all domains that have ever pointed to a given IP. This is far more comprehensive than a PTR lookup and reveals the full picture of shared hosting.
For a deeper dive into PTR records and traditional reverse DNS, read our Reverse DNS Guide.
What ASN Data Reveals About Hosting Infrastructure
Every IP address belongs to an Autonomous System (AS), identified by an ASN (Autonomous System Number). When you look up an IP on reverseips.com, we display the associated ASN and organization name. This information tells you:
- Which hosting provider or ISP controls the IP block
- Whether the IP belongs to a major cloud provider (AWS, Google, Azure), a CDN (Cloudflare, Fastly), or a traditional hosting company
- The geographic region associated with the network allocation
ASN data is invaluable for threat intelligence. If you see hundreds of suspicious domains on a single IP within a small hosting provider's ASN, that is a strong indicator of a bulletproof hosting operation or compromised server.
Related Tools for DNS and IP Intelligence
- IP History – Track how a domain's IP address has changed over time. Useful for detecting hosting migrations and infrastructure changes.
- DNS Timeline – Visualize the complete DNS record history for any domain, including A, AAAA, MX, NS, and TXT records.
- Internet Live View – Real-time BGP monitoring and internet routing intelligence.
- Profundis.io – The full DNS intelligence platform with unlimited queries, historical data, and API access.
Start Your Reverse IP Lookup
Ready to discover what domains share an IP? Head to the reverseips.com homepage and enter any IP address. For programmatic access and advanced features, explore the Profundis.io API.