FA-7176 / Network routing / Open access

Link local destination requires interface scope · case 01

Link local destination requires interface scope.

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

ROOT CAUSE

The faulty implementation uses `True` for the link-local-destination-requires-interface-scope decision.

VERIFIED REPAIR

Apply the explicit link-local-destination-requires-interface-scope contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `interface is not None` and still violates a separate fixture.

Case contract

Bounded offline decision model: link local destination requires interface scope. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.

Why this case matters

This deterministic network routing model isolates the link-local-destination-requires-interface-scope 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(link_local, interface):
    return True
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, None), False)", "check('fixture 2', solve(False, None), True)", "check('fixture 3', solve(True, 'eth0'), True)", "check('fixture 4', solve(False, 'eth0'), 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`	`True`	Passed
fixture 3	`True`	`True`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`True`	`False`	Failed

SHA-256 / 9cfa44a7848cca673db7c889e1e383dc7b0afcd95967baf7cce9a161a06e58ec

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(link_local, interface):
    return interface is not None
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, None), False)", "check('fixture 2', solve(False, None), True)", "check('fixture 3', solve(True, 'eth0'), True)", "check('fixture 4', solve(False, 'eth0'), 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`	`True`	Failed
fixture 3	`True`	`True`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`False`	`False`	Passed

SHA-256 / 6168febc60fbd80344ed29a432d9db53eda54c5eddcd05fe7c83f784b7e9bfdd

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(link_local, interface):
    return not link_local or interface is not None
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, None), False)", "check('fixture 2', solve(False, None), True)", "check('fixture 3', solve(True, 'eth0'), True)", "check('fixture 4', solve(False, 'eth0'), 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`	`True`	Passed
fixture 3	`True`	`True`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`False`	`False`	Passed

SHA-256 / c60dfd0ba89d99023a39870eae6f0d151e729f16f9ace30f3665567227179990

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 2026-09-29T14:38:09.116461+00:00.

Case digest / c6c546ce709e2c077df26cc819828cf3e9b9568b6ca8132de607a775306b2660