FA-7326 / Transport flow control / Open access
Ip forwarding expires a packet before hop limit underflows · case 01
Ip forwarding expires a packet before hop limit underflows.
ROOT CAUSE
The faulty implementation uses `ttl-1` for the ip-forwarding-expires-a-packet-before-hop-limit-underflows decision.
VERIFIED REPAIR
Apply the explicit ip-forwarding-expires-a-packet-before-hop-limit-underflows contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `max(0,ttl-1)` and still violates a separate fixture.
Case contract
Bounded offline decision model: ip forwarding expires a packet before hop limit underflows. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.
Why this case matters
This deterministic transport flow control model isolates the ip-forwarding-expires-a-packet-before-hop-limit-underflows 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(ttl):
return ttl-1
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(1), None)", "check('fixture 2', solve(0), None)", "check('fixture 3', solve(2), 1)", "check('fixture 4', solve(64), 63)"]
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 | -1 | None | Failed |
| fixture 3 | 1 | 1 | Passed |
| fixture 4 | 63 | 63 | Passed |
| fixture 1 | 0 | None | Failed |
SHA-256 / 9a65a219d407abbf1fd03efe905bc73830b23241e083151287059463950f5b6a
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(ttl):
return max(0,ttl-1)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(1), None)", "check('fixture 2', solve(0), None)", "check('fixture 3', solve(2), 1)", "check('fixture 4', solve(64), 63)"]
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 | 0 | None | Failed |
| fixture 3 | 1 | 1 | Passed |
| fixture 4 | 63 | 63 | Passed |
| fixture 1 | 0 | None | Failed |
SHA-256 / e89d35c4349831cf2e060caec0a80f536fa1f66cd56e1a199c2a549aa42b73b7
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(ttl):
return ttl-1 if ttl>1 else None
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(1), None)", "check('fixture 2', solve(0), None)", "check('fixture 3', solve(2), 1)", "check('fixture 4', solve(64), 63)"]
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 | None | None | Passed |
| fixture 3 | 1 | 1 | Passed |
| fixture 4 | 63 | 63 | Passed |
| fixture 1 | None | None | Passed |
SHA-256 / 171f550d2b6b2f3463d4f5b27e04df6976e6725175625f95b8b4166f1c14ff7e
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 2026-09-29T14:38:10.690874+00:00.
Case digest / 170c9de2b7d3fa1a31335484c1335770c669af66192aa8fe7169d1d94b352135