FA-7426 / DNS resolution / Open access

Dns edns payload negotiation respects both peer and local cap · case 01

Dns edns payload negotiation respects both peer and local cap.

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

ROOT CAUSE

The faulty implementation uses `advertised` for the dns-edns-payload-negotiation-respects-both-peer-and-local-cap decision.

VERIFIED REPAIR

Apply the explicit dns-edns-payload-negotiation-respects-both-peer-and-local-cap contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `max(advertised,local)` and still violates a separate fixture.

Case contract

Bounded offline decision model: dns edns payload negotiation respects both peer and local cap. 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-edns-payload-negotiation-respects-both-peer-and-local-cap 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(advertised, local):
    return advertised
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(4096, 1232), 1232)", "check('fixture 2', solve(100, 1232), 512)", "check('fixture 3', solve(512, 1232), 512)", "check('fixture 4', solve(1232, 1232), 1232)"]
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	`100`	`512`	Failed
fixture 3	`512`	`512`	Passed
fixture 4	`1232`	`1232`	Passed
fixture 1	`4096`	`1232`	Failed

SHA-256 / b730a78492972fa60bd9b9f69bb7c466a23f1cf3c4db1a00474316c47ca03200

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(advertised, local):
    return max(advertised,local)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(4096, 1232), 1232)", "check('fixture 2', solve(100, 1232), 512)", "check('fixture 3', solve(512, 1232), 512)", "check('fixture 4', solve(1232, 1232), 1232)"]
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	`1232`	`512`	Failed
fixture 3	`1232`	`512`	Failed
fixture 4	`1232`	`1232`	Passed
fixture 1	`4096`	`1232`	Failed

SHA-256 / cd238b99ebad786fd8c7c98b4eec6adb557d412d90bea0d0d8777e5676fd6582

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(advertised, local):
    return min(max(512,advertised),local)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(4096, 1232), 1232)", "check('fixture 2', solve(100, 1232), 512)", "check('fixture 3', solve(512, 1232), 512)", "check('fixture 4', solve(1232, 1232), 1232)"]
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	`512`	`512`	Passed
fixture 3	`512`	`512`	Passed
fixture 4	`1232`	`1232`	Passed
fixture 1	`1232`	`1232`	Passed

SHA-256 / b8ee21fa473105cf1c316d86d9c882f78c64b3061e903f61213864890bc8aa7c

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 2026-09-29T14:38:11.810472+00:00.

Case digest / 7874426267131f0b2ce6e5d4988fa857aaaa2e8d76039c57bfd95952a6272270