Allocation Fragmentation Analyzer
Identify scattered free address blocks.
Allocation Fragmentation Analyzer: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
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How Allocation Fragmentation Analyzer Works?
The Allocation Fragmentation Analyzer works by listing every free block inside a parent range and comparing the largest free block with the total free space. A large gap between the 2 values means the free space is scattered.
Enter the parent block
Type the range to analyze, such as
10.70.0.0/22.Enter the allocations
Paste every allocated subnet.
Find the free blocks
The analyzer lists each free stretch as aligned CIDR blocks.
Score fragmentation
The analyzer reports the largest free block, the total free space, and the fragmentation index.
Allocation Fragmentation Analyzer Formula
The Allocation Fragmentation Analyzer formula is Fragmentation Index = 1 − (Largest Free Block ÷ Total Free Addresses).
Total free
F = Σ free block sizesAll unallocated addresses.
Largest free block
L = max(free CIDR block size)Biggest single allocatable prefix.
Fragmentation index
FI = 1 − L ÷ F0 = 1 contiguous block; near 1 = scattered.
Largest prefix available
32 − log2(L)Biggest subnet that can be allocated now.
Worked example: 10.70.0.0/22
Free total = 656 addresses in 10 blocks Largest = 128 (a /25) FI = 1 − 128 ÷ 656 = 0.80
Allocation Fragmentation Analyzer Conversion Table
The Allocation Fragmentation Analyzer conversion table lists every free block left in 10.70.0.0/22 after 6 scattered allocations.
| Free Block | Range | Addresses |
|---|---|---|
| 10.70.0.0/27 | 10.70.0.0 – 10.70.0.31 | 32 |
| 10.70.0.64/26 | 10.70.0.64 – 10.70.0.127 | 64 |
| 10.70.0.192/26 | 10.70.0.192 – 10.70.0.255 | 64 |
| 10.70.1.0/26 | 10.70.1.0 – 10.70.1.63 | 64 |
| 10.70.1.128/25 | 10.70.1.128 – 10.70.1.255 | 128 |
| 10.70.2.128/25 | 10.70.2.128 – 10.70.2.255 | 128 |
| 10.70.3.0/28 | 10.70.3.0 – 10.70.3.15 | 16 |
| 10.70.3.32/27 | 10.70.3.32 – 10.70.3.63 | 32 |
| 10.70.3.64/26 | 10.70.3.64 – 10.70.3.127 | 64 |
| 10.70.3.192/26 | 10.70.3.192 – 10.70.3.255 | 64 |
Allocated: 10.70.0.32/27, 10.70.0.128/26, 10.70.1.64/26, 10.70.2.0/25, 10.70.3.16/28, 10.70.3.128/26.
What is Allocation Fragmentation Analyzer?
The Allocation Fragmentation Analyzer is a tool that measures how scattered the free space in an address block is, and reports the largest subnet that can still be allocated.
A block can be half empty and still unable to fit a single /24. Small allocations placed without a plan break free space into pieces that are too small or badly aligned. The fragmentation index puts a number on that problem.
The analyzer supports decisions about consolidation: moving a few small subnets often frees a large aligned block.
What are the uses of Allocation Fragmentation Analyzer?
There are 4 main uses of the Allocation Fragmentation Analyzer, including consolidation planning, allocation policy, and capacity reporting.
Planning consolidation
The analyzer shows which small subnets block a large free prefix.
Setting allocation policy
High fragmentation supports a rule to allocate small blocks from a dedicated range.
Reporting real capacity
The largest free block is the true limit for new large requests.
Comparing regions
Regions with the same free total can have very different fragmentation.