IPv4 Single-Prefix Range Alignment Audit

Audit whether an arbitrary inclusive IPv4 range is exactly one aligned CIDR block; power-of-two length alone is insufficient.

Description

Audit whether an arbitrary inclusive IPv4 range is exactly one aligned CIDR block; power-of-two length alone is insufficient.

An arbitrary IPv4 range is exactly one CIDR block only when its size is a power of two and its start is aligned to that size.

When to use this tool

Audit whether an arbitrary inclusive IPv4 range is exactly one aligned CIDR block; power-of-two length alone is insufficient.

Prepare the supplied start, end 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 start, end. 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.singlePrefix, result.prefix. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.

Count inclusive addresses, test count AND (count minus one) for zero, and require start modulo count to be zero. If aligned, return prefix 32 minus log2(count); otherwise prefix is null.^[1]

Input field	Meaning and representation	Accepted input
start	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
end	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.singlePrefix	Flag for single prefix under the exact condition described above.
result.prefix	The prefix value under the stated formula or text convention.

json

{
  "input": {
    "start": "10.0.0.0",
    "end": "10.0.0.3"
  },
  "output": {
    "result": {
      "singlePrefix": true,
      "prefix": 30
    }
  }
}

Limitations and assumptions

A power-of-two size alone is insufficient. This does not find a multi-block cover or evaluate usable hosts.
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

Tool behavior and example: IPv4 Single-Prefix Range Alignment Audit — tool.io

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 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.