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Tablet link: DHCP lease 86400 s; a tablet NetworkStack update made the 15 s lease drop the link every 15 s
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz
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Mikkeli Matlock
2026-10-14 08:54:49 +09:00
parent fc9f93336e
commit 00ab54d538
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docs/impl/reports/USB-TABLET-LINK.md
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@@ -28,6 +28,25 @@ net_ipv4_defroute_router=192.168.55.100 net_ipv4_defroute_metric=32766
The Orin also adds `default via 192.168.55.100 metric 32766`. This ranks below everything else, so it never takes traffic from Ethernet, WiFi or LTE. The Orin also adds `default via 192.168.55.100 metric 32766`. This ranks below everything else, so it never takes traffic from Ethernet, WiFi or LTE.
### DHCP lease: 86400 s, not NVIDIA's 15 s (2026-10-14)
NVIDIA ships `net_dhcp_lease_time=15`. It worked while the tablet's Android stretched short leases and renewed every
~30 s. On 2026-10-14 the tablet's NetworkStack (Mainline module) updated itself (`lastUpdateTime 08:21:19`) and
began taking 15 s literally: the address expired, Android restarted `usb0`, and every WebSocket to svc-gw died on a
**15.0 s cycle** (`DHCPDISCOVER` every 15 s in the Orin's log, `connection lost` in svc-gw's, ~0.3 s to reconnect).
Now `net_dhcp_lease_time=86400` in the config file above; Android renews at 12 h. Safe on this link because:
- the pool is one address for one host at a time (a single USB-C port);
- the leases file is deleted on every plug-in: the udev rule `99-nv-l4t-usb-device-mode.rules` runs
`nv-l4t-usb-device-mode-state-change.sh`, which stops `nv-l4t-usb-device-mode-runtime` on unplug and starts it on
plug-in, and its start script recreates `/run/l4t-usb-devmode-dhcpd.leases` empty. A phone plugged in after the
tablet always gets the address.
Applied with `sudo systemctl restart nv-l4t-usb-device-mode-runtime.service` (the link drops for a few seconds).
The file is part of `nvidia-l4t-init`; a package update may restore 15. Sign: svc-gw logging `connection lost`
every 15 s while `DHCPDISCOVER` repeats.
## Android routes apps over it only when it is the default network ## Android routes apps over it only when it is the default network
The tablet joins the USB network, but Android only sends ordinary app traffic over its *default* network, and an Ethernet network without The tablet joins the USB network, but Android only sends ordinary app traffic over its *default* network, and an Ethernet network without