DNS Compression Pointer Target Audit
Audit an explicit DNS compression pointer against packet bounds, backward direction and independently supplied label boundaries; not pointer-chain decoding or loop proof.
Description
Audit an explicit DNS compression pointer against packet bounds, backward direction and independently supplied label boundaries; not pointer-chain decoding or loop proof.
A DNS compression pointer needs an eligible packet target. This audit separately exposes packet bounds, backward direction and a supplied label-boundary claim.1
When to use this tool
Audit an explicit DNS compression pointer against packet bounds, backward direction and independently supplied label boundaries; not pointer-chain decoding or loop proof.
- Prepare the supplied pointerPosition, target, packetBytes, labelBoundaries 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 pointerPosition, target, packetBytes, labelBoundaries. 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.inBounds, result.backward, result.labelBoundary, result.eligible. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Validate packetBytes, pointerPosition and the 14-bit target, plus each declared boundary. Set inBounds when target is below packetBytes, backward when below pointerPosition and labelBoundary when present in labelBoundaries. eligible is their conjunction.2
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| pointerPosition | pointer position. | Integer from 0 to packetBytes - 2 inclusive |
| target | target. | Integer from 0 to 16383 inclusive |
| packetBytes | packet bytes. | Integer from 0 to 65535 inclusive |
| labelBoundaries | label boundaries. | List of finite numbers; at most 128 entries |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.inBounds | Flag for in bounds under the exact condition described above. |
| result.backward | Flag for backward under the exact condition described above. |
| result.labelBoundary | Flag for label boundary under the exact condition described above. |
| result.eligible | Flag for eligible under the exact condition described above. |
{
"input": {
"pointerPosition": 20,
"target": 10,
"packetBytes": 30,
"labelBoundaries": [
10
]
},
"output": {
"result": {
"inBounds": true,
"backward": true,
"labelBoundary": true,
"eligible": true
}
}
}Limitations and assumptions
- Boundary evidence is caller supplied. No pointer is dereferenced, and eligible does not prove a complete pointer chain is valid or loop-free.
- 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 a packet-aware DNS parser or resolver when the task requires compression-chain validation, live records or complete resource-record semantics. Keep byte labels, presentation text and network packets distinct.
References
Similar or alternative tools
- DNS Compression Pointer Offset Formatter
Format an explicit 14-bit packet offset as a DNS compression pointer token; does not verify packet layout or target labels.
- DNS Compression Pointer Offset Parser
Parse exactly one two-byte DNS compression pointer into its 14-bit packet offset; does not dereference the pointer.