IPv4 Prefix Pair Common Ancestor
Return the smallest IPv4 prefix containing two complete normalized prefixes; it may include additional addresses beyond their union.
Description
Return the smallest IPv4 prefix containing two complete normalized prefixes; it may include additional addresses beyond their union.
A common ancestor of two IPv4 prefixes must cover each complete block, not just their input address spellings.
When to use this tool
Return the smallest IPv4 prefix containing two complete normalized prefixes; it may include additional addresses beyond their union.
- Prepare the supplied left, leftPrefix, right, rightPrefix 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, leftPrefix, right, rightPrefix. 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 both prefixes. Choose the minimum of their prefix lengths and the shared leading bits of their normalized starts, then return the normalized ancestor.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 |
| leftPrefix | left prefix. | Safe integer |
| 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 |
| rightPrefix | right prefix. | Safe integer |
| 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": {
"left": "10.0.0.0",
"leftPrefix": 25,
"right": "10.0.0.128",
"rightPrefix": 25
},
"output": {
"result": {
"address": "10.0.0.0",
"prefix": 24
}
}
}Limitations and assumptions
- The result ignores routing attributes, policy and allocation ownership. It need not preserve unrelated route semantics.
- 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 Address Pair Common Prefix
Find the exact common leading-bit prefix of two IPv4 addresses; identical addresses yield a /32 ancestor.
- IPv4 Prefix Child Pair
Split a normalized IPv4 CIDR into its two equal immediate child prefixes; /32 leaves have no children and are rejected.