CIDR Aggregator & Splitter
Aggregate overlapping IPv4/IPv6 CIDRs and ranges without adding uncovered addresses. Exclude ranges or split exact coverage into fixed-prefix subnets.
Aggregate exact address coverage
Paste one CIDR, bare address or inclusive start–end range per line. Overlapping and adjacent intervals are merged and then covered by the smallest aligned CIDR list. This preserves the exact union: non-contiguous ranges are not widened into a larger block that includes missing addresses.
The example merges two IPv4 /25 networks into 192.0.2.0/24 and two adjacent IPv6 /127 networks into 2001:db8::/126. IPv4 and IPv6 are calculated separately with integer precision; their exact address totals are returned as decimal strings. Host bits in CIDR inputs are normalized.
Exclude or split without silent widening
Exclusion mode subtracts the second list from the input union, then returns an exact CIDR cover of what remains. An empty result is valid. Split mode requires every output block to fit the requested prefix exactly; a prefix that would widen a range is rejected. Use one address family at a time when splitting.
Limits are 1,000 input lines per list, 200,000 characters per field and 4,096 output CIDRs. A split exceeding the limit is rejected before addresses or subnets are materialized. No addresses are probed and no routing policy is installed. The existing subnet calculator remains the place for individual subnet masks, address classification and host-count questions.
Reference
Questions & answers
Can separated /24 blocks become one /23?
Only if their union is contiguous and aligned to that /23. Otherwise the exact CIDRs remain separate.
Does this enumerate IPv6 hosts?
No. It works with interval boundaries and CIDR blocks, so large IPv6 spaces retain exact totals without expanding every address.
Is my input uploaded?
No. Parsing and generation run in your browser. Engines and datasets load from this site; the tool does not store input or send it to a processing API.