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Record LTE failover test: seamless switch, Tailscale direct over IPv6

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With the WiFi radio off, the default route moved to wwan0 within 10 s and
all IPv4/DNS/Tailscale samples passed. Tailscale went direct to halogen
over povo's global IPv6 (no DERP), and an SSH session over the tailnet
survived both switches. WiFi took back IPv4 within 15 s and IPv6 within
~45 s.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
mikkeli
2026-10-08 09:50:18 +09:00
parent 787c414c0a
commit e29c20de75
1 changed files with 18 additions and 0 deletions
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docs/impl/reports/SIM7600-SETUP.md
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@@ -106,6 +106,24 @@ ip route show default # wlP1p1s0 metric 600, wwan0 metric 1000
curl --interface wwan0 https://ifconfig.me
```
### Failover test (2026-10-08)
Ran `/usr/local/sbin/lte-failover-test.sh` as a detached unit (`systemd-run --unit=lte-failover-test`). It turns the WiFi radio off for 180 s,
samples every 10 s, then turns it back on, logging to `/var/log/lte-failover-test.log`. A `wifi-failsafe` timer (`systemd-run --on-active=10min nmcli radio wifi on`)
was armed first, so a broken LTE path couldn't lock out a remote session.
| Phase | Default route | Public IPv4 | Ping 1.1.1.1 | Tailscale → halogen |
|-------|---------------|-------------|--------------|---------------------|
| WiFi on | `wlP1p1s0` (600) | home ISP | ~12 ms | direct, LAN (3–4 ms) |
| WiFi off | `wwan0` (1000), within 10 s | KDDI `106.128.x.x` | 25–55 ms | **direct over IPv6** to halogen's home IPv6 (40–85 ms), no DERP relay |
| WiFi back | `wlP1p1s0`; IPv4 within 15 s, IPv6 within ~45 s (NM connectivity check) | home ISP | ~12 ms | direct, LAN |
Zero failed samples (IPv4, DNS, Tailscale ping). An SSH session over Tailscale stayed up across both switches.
Carrier CGNAT on IPv4 doesn't matter because povo gives a global IPv6 address, which Tailscale uses for a direct path.
Note: `wwan0` also gets a kernel-installed IPv6 RA default route at metric 1024. That still ranks below WiFi (600) and only wins during the
brief NM connectivity-check penalty (`+20000`) after WiFi returns.
### GNSS
- GNSS engine was already running (`AT+CGPS?` → `1,1`). Set to start on boot: `AT+CGPSAUTO=1` (persists in modem).