Subnet Summarization Calculator
Use the responsive calculator grid below. Large screens show three columns, medium screens show two, and mobile stacks to one.
Example Data Table
| Scenario | Input Networks | Exact Summary | Covering Supernet | Route Savings |
|---|---|---|---|---|
| Aligned campus blocks | 192.168.8.0/24, 192.168.9.0/24, 192.168.10.0/24, 192.168.11.0/24 | 192.168.8.0/22 | 192.168.8.0/22 | 4 routes to 1 route |
| Mixed alignment | 172.16.4.0/24, 172.16.5.0/24, 172.16.6.0/24, 172.16.7.0/24, 172.16.8.0/24 | 172.16.4.0/22, 172.16.8.0/24 | 172.16.0.0/20 | 5 routes to 2 exact routes |
Formula Used
- Network address = IP address AND subnet mask.
- Broadcast address = Network address OR wildcard mask.
- Wildcard mask = 255.255.255.255 XOR subnet mask.
- Total addresses = 232 - prefix.
- Usable hosts = Total addresses minus 2, except /31 and /32 special cases.
- Exact aggregation merges overlapping or adjacent ranges, then rewrites each merged span using the largest aligned CIDR blocks that fit exactly.
- Smallest covering supernet is found from the longest common prefix shared by the lowest network address and highest broadcast address.
How to Use This Calculator
- Paste IPv4 CIDR blocks or host addresses into the input box. Host addresses are treated as /32 unless you specify another prefix.
- Choose the summary mode. Use exact aggregation for precise routing. Use the covering option to test a one-route umbrella.
- Set the graph limit and optional analysis switches. Duplicate removal is useful when pasted route lists contain repeats.
- Click Summarize Subnets. The report appears above the form with normalized inputs, exact outputs, supernet analysis, and a Plotly graph.
- Use the CSV button for spreadsheet export and the PDF button for a printable summary report.
FAQs
1. What does subnet summarization do?
It combines multiple IPv4 routes into the smallest exact set of CIDR blocks, or into one covering supernet when you allow extra address space.
2. Do networks need to be consecutive?
Exact single-block summarization needs contiguous ranges and correct binary alignment. Otherwise, the tool still works but returns multiple summarized routes.
3. Why was my entry changed after submission?
If you enter a host inside a subnet, the tool resets host bits to the correct network boundary. Example: 192.168.10.44/24 becomes 192.168.10.0/24.
4. What is a covering supernet?
A covering supernet is the smallest one-route umbrella that contains every entered subnet. It can include addresses you did not list.
5. Can overlapping subnets be summarized?
Yes. The tool normalizes, sorts, and merges overlapping or duplicated ranges before summarizing them, which keeps the report accurate.
6. How are /31 and /32 networks handled?
The tool keeps /31 and /32 valid. It reports two addresses for /31 point-to-point links and one address for /32 host routes.
7. When should I avoid a covering supernet?
Avoid a covering supernet when extra addresses could create routing leaks, policy issues, or unwanted traffic attraction. Use exact aggregation instead.
8. What does the graph show?
The graph compares address counts for normalized inputs and summarized outputs. It makes consolidation and block sizes easier to review quickly.