FA-7441 / DNS resolution / Open access

Dns answer class must match question class · case 01

Dns answer class must match question class.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The faulty implementation uses `type_ok` for the dns-answer-class-must-match-question-class decision.

VERIFIED REPAIR

Apply the explicit dns-answer-class-must-match-question-class contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `question_class == answer_class` and still violates a separate fixture.

Case contract

Bounded offline decision model: dns answer class must match question class. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.

Why this case matters

This deterministic dns resolution model isolates the dns-answer-class-must-match-question-class policy at a network component boundary.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(question_class, answer_class, type_ok):
    return type_ok
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(1, 3, True), False)", "check('fixture 2', solve(1, 1, False), False)", "check('fixture 3', solve(1, 1, True), True)", "check('fixture 4', solve(3, 3, True), True)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
fixture 2	`False`	`False`	Passed
fixture 3	`True`	`True`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`True`	`False`	Failed

SHA-256 / 3412586d02d1e4bd68a3a44a793072093fd535e53e295de869defa6918271209

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(question_class, answer_class, type_ok):
    return question_class == answer_class
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(1, 3, True), False)", "check('fixture 2', solve(1, 1, False), False)", "check('fixture 3', solve(1, 1, True), True)", "check('fixture 4', solve(3, 3, True), True)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
fixture 2	`True`	`False`	Failed
fixture 3	`True`	`True`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`False`	`False`	Passed

SHA-256 / f7e72395440be47300184dcc1bce91c4ad3cab1dd3552dcd93a8bb323d1b4c80

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(question_class, answer_class, type_ok):
    return question_class == answer_class and type_ok
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(1, 3, True), False)", "check('fixture 2', solve(1, 1, False), False)", "check('fixture 3', solve(1, 1, True), True)", "check('fixture 4', solve(3, 3, True), True)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
fixture 2	`False`	`False`	Passed
fixture 3	`True`	`True`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`False`	`False`	Passed

SHA-256 / 35d789764c24055551edb07c5d2bcff4056d9ceed03b679f67d1a62b1650abcd

Verification & scope

Bounded deterministic policy model over validated inputs; not a complete protocol stack or an interoperability claim. The five variants rotate the same explicit fixture set. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:38:12.058746+00:00.

Case digest / f40287452327b9a1122aa9a1459e0e9348085a7f173e72227d596754ddccc8ff