CIDR Aggregate Calculator
Reduce IPv4 CIDR lists by removing redundancy and merging exact sibling blocks.
Summarize exact IPv4 CIDR coverage
CIDR aggregation reduces a list only when coverage remains exactly the same. This calculator normalizes every block, sorts ranges, removes entries already contained by another block, and repeatedly merges adjacent siblings that have equal prefixes and begin on their shared parent boundary. It continues until no additional exact merge is possible.
The default two /25 networks are aligned halves of 192.168.1.0/24, so they collapse to that single /24. Two equal-size blocks with a gap cannot merge, and adjacent blocks of different sizes remain separate unless later normalization creates matching siblings. Duplicate or fully covered entries disappear from the final list.
When two blocks can become one parent
Aggregation changes representation, not intended route attributes or security policy. Two prefixes may carry different next hops, communities, access rules, or ownership even when their address coverage forms a parent. Calculation stays in your browser and uses no routing table. Use the minimized list only where every merged address truly shares the same treatment and where summarization will not advertise unintended reachability.
Frequently Asked Questions
What conditions allow two CIDRs to merge?
They must have equal prefix length, be directly adjacent, and start on the boundary of their common parent.
Are contained or duplicate blocks removed?
Yes. A block already fully covered by an earlier normalized range is redundant and is removed.
Is a mathematically valid aggregate always safe to route?
No. Different policies or next hops can make an aggregate operationally incorrect even when coverage matches.
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