CIDR Aggregator – Merge & Summarize IP Ranges (Route Summarization)
Merge a list of IPv4 CIDR blocks into the smallest set of covering routes — with an exact-cover guarantee: no addresses added, none lost.
Aggregation results
6 blocks → 3 blocks after aggregation.
| Input blocks | Aggregated result(s) |
|---|---|
| 10.0.0.0/24 10.0.1.0/24 10.0.2.0/24 10.0.3.0/24 10.0.4.0/25 10.0.4.128/26 |
10.0.0.0/22 10.0.4.0/25 10.0.4.128/26 |
Resulting blocks (exact cover of your inputs):
How route summarization works
Routing tables grow with every block a network announces. When several adjacent ranges come from the same allocation — say a /24 handed out per floor — a router can advertise one supernet covering all of them, and every downstream device keeps just a single entry. The math is binary: a /23 covers two adjacent aligned /24s, a /22 covers four, and so on.
This tool finds the minimal such set for your exact list. It never pads a summary with addresses you did not provide: if your blocks are adjacent but not aligned to a larger boundary, or if gaps separate them, the output simply keeps the smallest cover that adds nothing beyond your inputs.
Related tools
Need the reverse direction? The IP range to CIDR converter turns any first/last address span into minimal blocks, and the subnet splitter divides a block into equal pieces the other way.
Frequently asked questions
Can aggregation include addresses not in my list?
Never. This tool produces an exact cover: the output blocks cover precisely the union of your input ranges — no extra addresses added, none left out. Blocks that cannot be summarized exactly are kept unchanged.
Why didn't 10.0.0.0/24 and 10.0.1.0/24 merge into /23?
They do: the two blocks are adjacent and aligned, so they collapse into a single 10.0.0.0/23. Merging requires both adjacency and alignment — the combined span must sit on a boundary matching the larger prefix. For example 10.0.1.0/24 and 10.0.2.0/24 are adjacent, but their span straddles a /23 boundary, so the tool correctly leaves both /24s in place.
What does route summarization do for BGP?
It lets a router announce one aggregate prefix instead of many component routes, shrinking the global routing table and cutting BGP update churn. Summarization only works when the component routes are contiguous and the cover is exact, which is exactly what this tool computes.
Does this merge overlapping blocks?
Yes. Overlapping blocks are merged into a single run and covered by the minimal set of CIDRs, and the tool lists each overlapping pair as a warning so you can audit your input.