IPv6 Prefix Address Offset
Return exact IPv6 zero-based address offset within a supplied normalized prefix, retaining null for nonmembers.
Description
Return exact IPv6 zero-based address offset within a supplied normalized prefix, retaining null for nonmembers.
An address has a prefix-relative offset only when it lies inside the normalized block. A null offset makes nonmembership explicit.
When to use this tool
Return exact IPv6 zero-based address offset within a supplied normalized prefix, retaining null for nonmembers.
- Prepare the supplied address, network, 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, network, 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.member, result.offset. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Normalize network at prefix, parse address and compare inclusive bounds. Return member plus decimal-text address minus network start, or null when outside.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 |
| 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 |
| prefix | prefix. | Safe integer |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.member | Membership flag for the specific set and boundary convention above. |
| result.offset | Exact zero-based offset under the stated address or byte convention; null where nonmembership is allowed. |
{
"input": {
"address": "::3",
"network": "::",
"prefix": 126
},
"output": {
"result": {
"member": true,
"offset": "3"
}
}
}Limitations and assumptions
- The tool does not infer assignment, reachability or usable-host status from membership.
- 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 Prefix Address at Offset
Select one IPv6 address at an exact zero-based offset inside a normalized prefix, including every address and avoiding 128-bit floating precision loss.
- IPv4 Address Prefix Offset
Return an address’s exact zero-based prefix offset only when it belongs to an explicitly normalized IPv4 network; outside offsets remain null.