IPv4 Prefix Subdivision at Index
Return one normalized IPv4 child prefix at an exact zero-based subdivision index without enumerating the full subdivision.
Description
Return one normalized IPv4 child prefix at an exact zero-based subdivision index without enumerating the full subdivision.
A parent IPv4 prefix can contain many equal-size child blocks. A zero-based child index selects one without enumerating the others.
When to use this tool
Return one normalized IPv4 child prefix at an exact zero-based subdivision index without enumerating the full subdivision.
- Prepare the supplied network, parentPrefix, childPrefix, index fields for this operation.
- Compare the complete example with the representation used by your own input before carrying the result into another step.
How to use the tool and how it works
- Enter network, parentPrefix, childPrefix, index. Use the exact text syntax, units and index conventions explained below.
- Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
- Read result.address, result.prefix. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Normalize network at parentPrefix. Require childPrefix from parentPrefix through 32 and decimal-text index below 2^(childPrefix minus parentPrefix). Add index times child block size to the parent start.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| network | Address text for the family named by this tool. Prefix lengths are separate fields where shown. | Text; at most 8,192 UTF-16 code units, subject to the grammar above |
| parentPrefix | parent prefix. | Safe integer |
| childPrefix | child prefix. | Integer from parentPrefix to 32 inclusive |
| index | Exact decimal integer text; keep it quoted in JSON rather than converting through a floating-point number. | Optional leading + or - and 1 to 256 decimal digits; no whitespace |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.address | The address value under the stated formula or text convention. |
| result.prefix | The prefix value under the stated formula or text convention. |
{
"input": {
"network": "10.0.0.0",
"parentPrefix": 24,
"childPrefix": 26,
"index": "2"
},
"output": {
"result": {
"address": "10.0.0.128",
"prefix": 26
}
}
}Limitations and assumptions
- This is a prefix block index, not a usable-host offset. Routing and allocation policies are not applied.
- IPv4 input uses strict dotted-decimal octets without leading zeros or surrounding whitespace. IPv6 accepts its supported compressed or full spellings and trims surrounding whitespace, but rejects zone identifiers; embedded dotted IPv4 uses the strict IPv4 spelling. IPv6 address outputs are fully expanded unless stated otherwise.
- All declared input fields are required and unexpected top-level fields are rejected. Numbers must be finite; lists are limited to 128 entries and ordinary text fields to 8,192 UTF-16 code units, with tighter limits where stated.
- JSON text inputs must parse within bounded nesting and size limits. Numeric outputs outside the safe finite range are rejected; large exact integer results use decimal strings. Indexes and half-open spans are zero-based unless a rank is explicitly described as one-based.
Alternative or Complementary methods
Use address-set arithmetic for prefix planning and a routing or interface inspection for deployed configuration. Membership and overlap do not establish reachability, ownership or route preference.
References
Similar or alternative tools
- IPv4 Prefix Subdivision Index
Locate a member IPv4 address’s normalized child-prefix index inside an explicit parent at a requested subdivision width.
- IPv4 Address Pair Common Prefix
Find the exact common leading-bit prefix of two IPv4 addresses; identical addresses yield a /32 ancestor.