CIDR Subnet Splitter
Split IPv4 networks into equal blocks by prefix or count
Split an IPv4 parent into equal subnets by prefix or a power-of-two count, up to 512 blocks. Count 1 preserves the parent. Rows show address ranges, not guaranteed assignable hosts. Combined input limit: 1 MiB.
Addresses and networks are processed in this page. No network probes or input drafts; analytics contains fixed action names and counts only.
The full guide also includes pitfalls, worked examples, snippets, FAQs, and related tools for checking results or troubleshooting.
About this tool
Divide an IPv4 CIDR into equal-sized child networks for an address-plan review. Choose a target prefix at least as long as the parent, or a power-of-two subnet count from 1 to 512. A /24 split into four blocks produces four /26 networks, each containing 64 addresses. Host bits in the parent are normalized before splitting and the original address remains in the summary. A count of one returns the unchanged parent; an impossible prefix beyond /32 is rejected. The output limit is 512 blocks, so choosing a smaller target prefix closer to the parent reduces the number of rows. Counts such as 2.9 or 3 are not rounded. Bounds include every address and do not guarantee platform-assignable host capacity. Processing is local, combined input is capped at 1 MiB, and no input draft is saved.
Scenario Recipes
Split a /24 into four reviewable blocks
Goal: Prepare equal ranges for four segments
- Enter 192.0.2.0/24, select Subnet count and enter 4.
- Run and verify /26 starts at .0, .64, .128 and .192.
- Check 64 addresses per block, then download TSV and apply any provider reservations separately.
Result: Four adjacent /26 ranges exactly cover the parent /24.
Failure Clinic (Common Pitfalls)
Increasing the prefix makes an oversized result larger
Cause: A longer target prefix creates smaller child blocks, so more are needed to cover the same parent.
Fix: Move the target prefix toward the parent prefix to reduce row count. The tool lists at most 512 children and rejects a larger request before building the table.
Equal subnet counts are confused with host requirements
Cause: A count of four asks for four equal CIDRs; it does not mean four hosts. Unequal department sizes need a different allocation model.
Fix: Choose a power-of-two block count and verify address capacity, or use VLSM for unequal requirements. Apply network, broadcast and platform reservations after choosing the blocks.
Production Snippets
Four equal children of a /24
text
Parent: 192.0.2.17/24 -> 192.0.2.0/24
Target prefix: 26; equivalently count: 4
192.0.2.0/26 -> .0β.63
192.0.2.64/26 -> .64β.127
192.0.2.128/26 -> .128β.191
192.0.2.192/26 -> .192β.255
64 addresses per block, 256 total.Frequently Asked Questions
How are prefix and count related?
Child count equals 2 raised to target prefix minus parent prefix. A /24 to /26 split gives 2^2 = 4 blocks; each /26 contains 64 addresses.
Why is a count of 3 rejected?
Equal CIDR subnets divide a parent by powers of two. Three equal aligned child CIDRs cannot cover it exactly. Use 4 equal blocks, or a variable-length planner for unequal allocations.
Does 2.9 become 2?
No. Counts and target prefixes must be complete decimal integers. Fractional values, signs, exponent notation and leading zeros are rejected without truncation.
How do I reduce an over-512 result?
Choose a smaller target prefix closer to the parent, or a smaller subnet count. Increasing a /16 target to /17 creates more blocks, not fewer.
Can a /31 split into two /32 networks?
Yes. Each resulting /32 contains exactly one address. This splitter reports address bounds and counts; it does not apply a traditional minus-two host count to the children.
Will a host address in the parent lose its offset?
The parent network is normalized deliberately. 192.0.2.17/24 is split from 192.0.2.0/24; the original 192.0.2.17 is shown separately so you can verify that normalization.
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