Tablet link: DHCP lease 86400 s; a tablet NetworkStack update made the 15 s lease drop the link every 15 s

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz
2026-10-14 08:54:49 +09:00
parent fc9f93336e
commit 00ab54d538
1 changed files with 19 additions and 0 deletions
@@ -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.

+### 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

 The tablet joins the USB network, but Android only sends ordinary app traffic over its *default* network, and an Ethernet network without