Two domains can look unrelated and still sit in the same block of 256 IP addresses. The Kwebby Class C IP Checker is a class c ip checker that takes a list of domains, resolves each to an IP address and shows the /24 block it belongs to. Domains that share a block get highlighted, so you can see hosting overlap in seconds. This guide explains what the results mean, and just as important, what they do not mean for Google rankings.
Key Takeaways
- The tool accepts domains separated by line breaks, commas or spaces, resolves each one and shows the IP address with its "Class C (/24)" block, such as 172.66.147.0/24.
- Rows that share a block turn amber, and a banner reports "N Class C IP subnet(s) are shared across multiple domains."
- A "Class C" block is the historical name for a /24 network of 256 addresses. SEO tools kept the name, although modern routing no longer uses address classes.
- Google's John Mueller said that "Link building by IP address seems futile and a bad use of time." A shared block is a hosting fact, not a penalty.
- Use the results to audit hosting spread across your own sites and to spot infrastructure overlap in a list of domains.
- The tool checks up to 20 unique domains per run and tells you when it skips the rest.
What Is the Kwebby Class C IP Checker?
The Kwebby Class C IP Checker is a free web tool that groups domains by network block. Paste your domains, click Check IPs and read a three-column table of domain, IP address and Class C block. Shared blocks stand out at a glance.
It belongs to Kwebby's Developer Tools. To get the IP for one domain without the grouping, use Domain Into IP.
Key Features and How It Works
Flexible domain input
The input box shows the placeholder "Enter domains one per line" with example.com, google.com and facebook.com as samples. The tool splits your text on line breaks, commas and spaces, so a pasted comma-separated list works. Full URLs also work: in our test, https://example.com/page was reduced to example.com.
One IP and one block per domain
For each domain the tool resolves the name with Google Public DNS, takes the first IPv4 (A) record and shows the block formed by its first three numbers. If a domain has several A records, only the first is compared. IPv6 addresses are not compared. The block appears as a.b.c.0/24, for example 172.66.147.0/24. A domain that does not resolve shows "N/A" in both columns.
Shared-block highlighting
When two or more domains fall in the same block, their rows turn amber and a warning appears above the table. In our run, example.com and www.example.com both resolved to 172.66.147.243, so the tool grouped them. example.net resolved to 172.66.175.59, which sits in a different block.
Progress message
While the lookup runs, the button reads "Checking…" and a spinner shows "Resolving IPs…". Results appear when every domain has an answer.
Why Class C Blocks Matter (and Where They Do Not)
The term comes from the early design of IPv4 addressing, which split the address space into classes. A Class C network covered 192.0.0.0 to 223.255.255.255 with a default prefix of /24, which leaves 256 addresses per network. Classless routing (CIDR) replaced address classes in 1993, but SEOs still use "Class C" as shorthand for a /24 block.
For years, link builders believed that links from sites in one block counted for less. Google staff say otherwise. In 2018, someone asked John Mueller whether a server's IP location affects rankings. He answered no, and added that a hosted CMS or a CDN can put a server anywhere.
What Google does act on is manipulation. Its spam policies describe link spam as buying or selling links for ranking, excessive link exchanges and automated link creation, and say advertising or sponsorship links are fine when qualified with rel="nofollow" or rel="sponsored". Those problems exist whatever the IP addresses are.
So treat the results as infrastructure data. A shared block means the sites live on the same host or network range. It does not show common ownership, because shared hosts and CDNs place unrelated sites in one range.
How to Use the Class C IP Checker
- Open the tool and click in the box that reads "Enter domains one per line".
- Paste your domains, one per line, or separate them with commas or spaces.
- Click "Check IPs". The button reads "Checking…" while the lookups run.
- Read the "Domain", "IP Address" and "Class C (/24)" columns.
- Look for amber rows and read the warning above the table for the number of shared blocks.
- Note any "N/A" rows, then re-check those names with Find DNS Records.
Best Practices for Reading the Results
Use exact host names
Enter the host name that appears in the link or in your DNS, such as www.example.com. The www version and the bare domain can resolve to different servers, and the table treats each name separately.
Read shared blocks as hosting facts
A shared block tells you about hosting, so use it for hosting decisions. If every site you run sits in one block, one provider outage affects all of them. That is a reliability point, not a ranking one.
Add a second signal before drawing conclusions
If a cluster of linking domains shares a block, look at the content, the link patterns and the ownership records. The Reverse IP Domain Checker lists other domains on the same address, and the WHOIS Checker shows registration details.
Re-check after a change
Hosting moves and CDN changes alter IPs. Run the list again after a migration to confirm where each domain now resolves.
Work in lists of 20
The tool checks the first 20 unique domains in your list and shows a note with the number it skipped. Split larger lists into batches.
Common Use Cases
- Hosting audits. Check whether your own sites, or a client's, are all in one block.
- Migration checks. Confirm that moved domains resolve to the new host range.
- Link prospect review. Spot prospects hosted together and look closer at how they relate.
- Backlink reviews. Group the domains from a Backlink Checker export by block when you look for patterns worth a manual review.
- Network documentation. Keep a record of which domains sit where.
Related Kwebby Tools
Domain Into IP converts domain names into IP addresses. The Reverse IP Domain Checker finds domains hosted on one IP. The Bulk GEO IP Locator shows the country, city and ISP behind a list of IPs. Find DNS Records displays the DNS entries for a domain, and the Backlink Checker lists links pointing at a site.
Frequently Asked Questions (FAQs)
What is a Class C IP address?
A Class C IP address is an IPv4 address in the old Class C range, 192.0.0.0 to 223.255.255.255, where the first three numbers identify the network. In SEO, "Class C" usually means the /24 block that shares the first three numbers. Each block holds 256 addresses.
Is 192.168.1.1 a Class C address?
By the old classes, yes, because 192.168.1.1 falls inside the Class C range. It is also a private address for local networks, so it does not point to a public website.
What is a Class C subnet mask?
The default Class C mask is 255.255.255.0, which is the same as a /24 prefix. It leaves the last number free for 256 addresses in the block.
Does Google penalize links from the same Class C IP?
Google has not said so. John Mueller has called link building by IP address futile, and he has said server location can be anywhere. Google's spam policies target link schemes, not IP ranges.
How many domains can I check at once?
Keep each list to 20 domains. The tool checks the first 20 unique domains and shows how many it skipped.
Is the Class C IP Checker free?
Yes. Kwebby states that the tool is completely free and needs no account.
Final Thoughts
The Class C IP Checker answers one clear question: which of these domains share a /24 block? Use that answer for hosting audits, migration checks and a first look at a list of linking sites, not as a ranking formula. Paste your own domains first, see how spread out your hosting is, then take any clusters to the Reverse IP Domain Checker for a closer look.