IPv6 Explicit Field Replacer
Replace an exact IPv6 bit field with least-significant-bit offset zero, preserving all unmasked address bits; no assignment or routing semantics.
Description
Replace an exact IPv6 bit field with least-significant-bit offset zero, preserving all unmasked address bits; no assignment or routing semantics.
Replacing a low-level IPv6 field requires an explicit bit offset and width. Bits outside the selected mask must remain intact.
When to use this tool
Replace an exact IPv6 bit field with least-significant-bit offset zero, preserving all unmasked address bits; no assignment or routing semantics.
- Prepare the supplied address, offset, width, value 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, offset, width, value. 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. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
offset ranges from 0 to 128 and width from 0 to 128 minus offset. Interpret value as nonnegative decimal integer text fitting width bits. Clear that mask in the address, insert value at the least-significant-bit-based offset and return fully expanded IPv6 text.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 |
| offset | offset. | Integer from 0 to 128 inclusive |
| width | width. | Integer from 0 to 128 - offset inclusive |
| value | 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. |
{
"input": {
"address": "::abcd",
"offset": 0,
"width": 8,
"value": "1"
},
"output": {
"result": {
"address": "0000:0000:0000:0000:0000:0000:0000:ab01"
}
}
}Limitations and assumptions
- A zero-width field accepts only zero and leaves the address unchanged. No interface-identifier, assignment or routing meaning is inferred.
- 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
- IPv6 Hextet Field Extractor
Extract one zero-based IPv6 hextet in network order after existing address parsing; returns its exact 16-bit numeric value.
- IPv6 Low Bit Field Extractor
Extract an explicitly sized low-bit IPv6 field as decimal integer text, including zero-width zero; no interface-identifier semantics inferred.