IPv4 Supernetting Calculator
Aggregate IPv4 CIDR networks without adding addresses. Compare the smallest covering prefix, its capacity and additional ranges with this local calculator.
Reduce a list of IPv4 networks to exact prefixes, then compare the smallest covering block. These two results serve different purposes.
Input
Enable JavaScript to calculate locally in your browser. Your input is not sent to a server.
Results
Enter the networks to aggregate.
Exact CIDR aggregation
This list covers exactly the input addresses without adding any.
- Input networks
- Unique networks
- Duplicates removed
- Contained networks removed
- Final prefixes
- Distinct IPv4 addresses
Smallest covering prefix
- Covering prefix capacity
- Additional addresses
Additional ranges (inclusive endpoints)
Warning: this covering prefix adds addresses. It is not equivalent to the exact aggregation. Review the additional ranges before copying it.
Exact covering prefix: no additional addresses.
Understanding the results
Exact aggregation
192.168.0.0/25 and 192.168.0.128/25 combine exactly into 192.168.0.0/24: the same 256 addresses remain covered. The calculation removes duplicates and contained networks, then merges aligned sibling blocks.
Covering prefix
192.168.0.128/25 and 192.168.1.0/25 cannot merge exactly. Their covering prefix, 192.168.0.0/23, contains 512 addresses, including 256 additional ones. Review the added ranges before using it.
Input and limits
Enter one aligned IPv4 CIDR network per line, without comments or decimal subnet masks; /0 to /32, up to 1,000 nonempty lines and 65,536 UTF-16 code units. Unaligned addresses are rejected with a suggestion, never corrected automatically. Calculations stay local.
Frequently asked questions
What is IPv4 supernetting?
Supernetting summarizes several IPv4 networks using less specific CIDR prefixes. Here, exact aggregation strictly preserves the address set: two aligned sibling /25 blocks can become a /24 without adding any addresses.
How does exact aggregation differ from a covering prefix?
Exact aggregation returns a minimal list covering only the original addresses. The covering prefix is a single block containing all those addresses, but may add others. The calculator reports the additional count and ranges separately.
Why can two adjacent networks not always be merged?
They must have equal sizes and share a correctly aligned CIDR parent. 192.168.0.128/25 and 192.168.1.0/25 are adjacent but are not siblings: replacing them with a single prefix would introduce additional addresses.
How are duplicates and contained networks handled?
A repeated CIDR contributes to coverage only once. A network already contained in a larger input network is removed as well. Separate counters report these removals; the total counts distinct addresses without double counting.
What do /31 and /32 mean in this calculator?
A /31 represents two addresses and a /32 represents one. Aggregation counts all addresses rather than usable hosts: it subtracts neither network nor broadcast addresses. It does not determine whether an address is assignable in your environment.
Why can a covering prefix include additional addresses?
A CIDR block is aligned and has a power-of-two size. The smallest block containing the extremes can therefore cover gaps between networks, or addresses before and after them. The additional ranges are the exact difference, with inclusive endpoints.
Can the result be applied directly to a routing configuration?
No: mathematical validity guarantees neither compatible destinations nor compliance with routing policies. Check next hops, prefix ownership, filters and potential black holes. A covering prefix that adds addresses requires particular care.