IPv6 Address Shared Leading Bits
Count shared leading bits of two exact IPv6 addresses; identical addresses share all 128 bits and no prefix is inferred from textual abbreviation.
Description
Count shared leading bits of two exact IPv6 addresses; identical addresses share all 128 bits and no prefix is inferred from textual abbreviation.
Two IPv6 addresses share a leading bit prefix before their first differing bit. Comparing integers avoids textual compression differences.
When to use this tool
Count shared leading bits of two exact IPv6 addresses; identical addresses share all 128 bits and no prefix is inferred from textual abbreviation.
- Prepare the supplied left, right 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 left, right. 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.bits. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Parse both 128-bit addresses, XOR them and subtract the XOR bit length from 128. Identical addresses return 128.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| left | 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 |
| right | 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 |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.bits | The bits value under the stated formula or text convention. |
{
"input": {
"left": "::1",
"right": "::3"
},
"output": {
"result": {
"bits": 126
}
}
}Limitations and assumptions
- The count describes only this address pair. It does not infer a configured subnet or route aggregation policy.
- 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
- Integer String IPv6 Address
Format an exact unsigned 128-bit decimal integer as fully expanded lowercase IPv6 using the existing group formatter.
- IPv6 Address Integer String
Convert an IPv6 address through the existing RFC 4291 parser to an exact unsigned 128-bit decimal integer string; no unsafe numeric conversion.