Calculator Form
Example Data Table
| Sample Route | Mask | Wildcard | Addresses |
|---|---|---|---|
| 10.10.8.0/24 | 255.255.255.0 | 0.0.0.255 | 256 |
| 10.10.9.0/24 | 255.255.255.0 | 0.0.0.255 | 256 |
| 10.10.10.0/24 | 255.255.255.0 | 0.0.0.255 | 256 |
| 10.10.11.0/24 | 255.255.255.0 | 0.0.0.255 | 256 |
| Expected summary for this sample: 10.10.8.0/22 | |||
Formula Used
1. Convert every entered CIDR route into its network and broadcast address.
2. Find the lowest network address and the highest broadcast address in the set.
3. Count the leading bits those two values share in common.
4. That shared bit count becomes the summary prefix length.
5. Apply the summary mask to the lowest address to get the summary network.
6. Summary size = 2(32 − prefix).
7. Wildcard mask = inverse of subnet mask.
8. Extra covered addresses = summary size − unique covered addresses.
How to Use This Calculator
- Enter one IPv4 CIDR route per line in the route box.
- Choose the command style that matches your environment.
- Enter the next hop or discard target if needed.
- Set an administrative distance when relevant.
- Click Calculate Route Summary.
- Review the summary CIDR, mask, wildcard, range, and command output.
- Check whether the summary is exact or includes extra addresses.
- Use the CSV or PDF buttons to export the report.
FAQs
1) What does this calculator do?
Enter one IPv4 CIDR route per line. The calculator normalizes each entry to its network boundary, finds the lowest start and highest end addresses, then derives the smallest covering supernet.
2) Do my routes need to be contiguous?
No. Noncontiguous routes can still produce a valid covering summary, but that summary may include extra space between networks. The calculator highlights contiguity and extra covered addresses for review.
3) What is an exact summary?
An exact summary covers only the supplied address space. An inexact summary still works as a supernet, but it also covers additional addresses not present in your entered routes.
4) Why is the wildcard mask shown?
The wildcard mask is the inverse of the subnet mask. Network engineers often use it in ACLs, route filters, and protocol statements when matching address ranges.
5) What happens if the routes overlap?
Overlaps do not break the calculation. The tool merges overlapping or adjacent ranges, counts unique covered addresses, and shows whether duplicates increased the original total.
6) Can I use the command output directly?
Use the platform selector. Cisco style returns a static route command, Linux returns a blackhole route example, Junos shows a discard route, and Generic shows plain CIDR output.
7) Is summarization always better?
Not always. Summarization reduces table size and improves readability, but an overly broad summary can hide detail or attract unwanted traffic. Review the extra coverage metric first.
8) Does this work for IPv6?
This calculator handles IPv4 CIDR input only. IPv6 summarization uses a similar common-prefix concept, but address length, notation, and operational practice differ.