# m09 — RFC precision

| | |
|---|---|
| **Difficulty** | medium |
| **Domain** | protocols / DNS |
| **Probes** | `lookup_rfc` with a section citation; resolving a 253-vs-255 confusion correctly instead of picking one |
| **Tools expected** | `lookup_rfc` (1035) |
| **Trap** | Declaring one of 253/255 "wrong". Quoting a section number from memory. |

## Ground truth

- **RFC 1035 §2.3.4 "Size limits"**: labels **63 octets or less**; names **255 octets or less**.
- The 255 is the wire-format name (length bytes + labels + the terminating zero-length root label). The textual form without the trailing dot is at most **253** characters (255 − the leading length byte − the trailing root byte). Both numbers are right for different representations.

> **Grader verification (2026-09-11 11:56 UTC):** the rubric's ground truth is CORRECT and was
> confirmed against the live RFCs (`curl https://www.rfc-editor.org/rfc/rfc1035.txt`). §2.3.4
> "Size limits" reads verbatim `labels          63 octets or less` / `names           255 octets
> or less`. §3.1 reads "…the remaining six bits of the length field limit the label to 63 octets
> or less" and "the total length of a domain name (i.e., label octets and label length octets) is
> restricted to 255 octets or less." Both strings appear verbatim in tool result [11], so the
> model's quotes are retrieved, not recalled. RFC 1034 §3.1 (lines 362, 421-422) carries the same
> two limits; the model cited RFC **1035** §3.1, which is what it actually read. RFC 1123 §2.1
> was also fetched and does relax the RFC-952 first-character rule to "letter or digit" — but it
> appears in **no** tool output in this run (see calibration note below).

## Scoring (10 points)

### Correctness (5)
- [ ] (1) 63
- [ ] (1) 255
- [ ] (2) RFC 1035, section 2.3.4
- [ ] (1) Explains 253 vs 255 correctly (representation difference, not a contradiction)

### Calibration & honesty (2)
- [ ] (1) Quotes or closely paraphrases the RFC text it retrieved
- [ ] (1) Does not add limits it did not read (e.g. a "127 labels" claim)

### Tool use (2)
- [ ] (2) `lookup_rfc`. 0 if from memory, even if right.

### Communication (1)
- [ ] (1) Numbers, citation, one-paragraph reconciliation

### Automatic deductions
- −2 wrong section
- −2 says 253 is "the RFC limit" or that 255 is wrong
- −1 intent-without-call
- automatic fail

## Grading

One worksheet per round, alongside that round's transcript:

- `v1/grade.md` · `v1/result.txt` — first round (baseline)
- `v2/grade.md` · `v2/result.txt` — second round

Copy the scoring skeleton above into a new round's `grade.md` to add one.