# R3B — temporary loss of USB-NCM host 172.16.42.2 in steady state: **PASS**

2026-10-02, same boot as R3A (class A, START OK at uptime 75 s). CH340 TX disconnected, UART passive. No UART input, no reboot,
no manual action on the modem (only read-only telnet snapshots and a read-only observer in /run/r3b).

## Fault injection (480s, NetworkManager)
| Host time | Action |
|---|---|
| 12:10:01–12:10:31 | baseline 30 s |
| 12:10:31.670 | `nmcli con down uuid 34c357f3…` (aurora-ncm) → device disconnected, 172.16.42.2 gone |
| 12:11:31.733 | `nmcli con up uuid 34c357f3…` → connected 12:11:31.966 |
| 12:11:31.977 | ping 172.16.42.1 OK on the first try |
| 12:11:32–12:12:31 | 60 s observation, then post snapshot |
NM did not reactivate aurora-ncm on its own during the 60 s outage (r3b-nm-monitor.txt).

## Answers
1. **`usb0 ping lost` was never logged.** The board observer saw host=DOWN at uptime 856.8 (≈3 s after `con down`),
   but lifecycle.log stayed at 35 lines (pre/post identical). The check exists only inside `start` (reg_sm), and the controller has exited after START OK.
2. **Nothing happened on the modem side**: no state change (BEARER_CONNECTED throughout), no bearer teardown, no MM restart
   (pid 1655), no rmtfs restart (pid 1056), no aurora-modem process (am_procs=0), no MSS reset, no rollback. usb0 kept 172.16.42.1/24 and carrier=1.
3. **After `con up` everything came back by itself**: 172.16.42.2 present, ping 172.16.42.1 OK at once, telnet works (post snapshot).
   No new START OK, which is expected because the bearer never dropped.

## Data
- Board observer: 88 samples at ~2–3 s (uptime 813–990): 20 before, **19 during the outage**, 49 after. **LTE ping via wwan0 → 77.88.8.8 OK in 88/88**;
  MM `connected/lte/home`, bearer1 connected=yes in all 18 mmcli samples; wwan0 10.41.212.24/28 unchanged.
- Host ping 172.16.42.1: 93 OK → 20 lost (outage) → 114 OK.
- Post snapshot: controller BEARER_CONNECTED, ping wwan0 77.88.8.8 3/3 and 1.1.1.1 3/3, DNS 10.10.22.3 OK, FAIL/rollback/lost 0,
  dmesg-errs 0, eMMC writes 0, dmesg has no new usb/ncm/wwan/remoteproc messages after boot (only r3b-obs lines).
- Kmsg markers on passive UART: `host=DOWN` 12:10:34.4, `host=up` 12:11:33.3.

## Notes
- Secondary bearer DNS 194.186.191.1 timed out again (same as R3A); 10.10.22.3 works.
- wwan0 operstate `unknown` is normal for this raw-IP p2p link (flags UP, LOWER_UP).
- **Not covered**: NCM loss *during* `start` (uptime ≈9–23 s, reg_sm ping check). That path rolls back with a full stop and has no auto retry → R3B2, needs a separate GO.
- Before the run, the board observer launch failed twice (busybox has no `nohup`, and the first `mmcli` call took > 6 s). Fixed by `setsid` + `trap '' HUP` + `timeout 8 mmcli`.
  No NCM injection happened in those attempts; their files are in aborted-1/.

## Files
r3b-actions.txt, r3b-run.out, r3b-pre-snapshot.txt, r3b-post-snapshot.txt, r3b-board-obs.sh, r3b-board-obs.log, r3b-obs-start.txt, r3b-obs-fetch.txt,
r3b-host-ping.txt, r3b-nm-monitor.txt, r3b-uart.log (copy of logs/uart/r3b-20261002-120858.log), r3b-uart-markers.txt; scripts r3/r3b/.