IPv6 Prefix Sibling
Return the same-size IPv6 sibling prefix under the immediate parent, toggling the lowest network bit; /0 has no sibling.
Description
Return the same-size IPv6 sibling prefix under the immediate parent, toggling the lowest network bit; /0 has no sibling.
Two same-size sibling IPv6 prefixes partition one immediate parent. Toggling the lowest network bit identifies the other child.
When to use this tool
Return the same-size IPv6 sibling prefix under the immediate parent, toggling the lowest network bit; /0 has no sibling.
- Prepare the supplied address, prefix 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 address, prefix. 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.
Require prefix from 1 to 128, normalize address and XOR the network start with the prefix block size. Return that expanded address and the unchanged prefix length.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| address | 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 |
| prefix | prefix. | Integer from 1 to 128 inclusive |
| 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": {
"address": "::2",
"prefix": 127
},
"output": {
"result": {
"address": "0000:0000:0000:0000:0000:0000:0000:0000",
"prefix": 127
}
}
}Limitations and assumptions
- The root /0 has no sibling and is rejected. No route or interface is changed.
- 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 Sibling
Find the other same-size child of an IPv4 prefix’s parent by toggling the lowest network bit; /0 has no sibling.
- IPv6 Nibble Prefix Length Check
Check IPv6 prefix alignment for whole-nibble reverse-zone labels; nonaligned prefixes do not imply a simple reverse-zone delegation.