Deprioritize iPhone USB tethering below Wi-Fi#5434
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alansikora wants to merge 1 commit intobasecamp:masterfrom
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Deprioritize iPhone USB tethering below Wi-Fi#5434alansikora wants to merge 1 commit intobasecamp:masterfrom
alansikora wants to merge 1 commit intobasecamp:masterfrom
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Pull request overview
This PR prevents iPhone USB tethering (via the ipheth kernel driver) from taking over the system default route when an iPhone is plugged in, by lowering its routing priority below Wi‑Fi using a NetworkManager config drop-in.
Changes:
- Add a NetworkManager drop-in that matches
driver:iphethand sets IPv4/IPv6 route metrics to 700. - Install the drop-in during fresh installs.
- Add a migration to deploy the drop-in on existing systems and reload NetworkManager.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
default/NetworkManager/conf.d/10-ipheth-low-priority.conf |
Adds a driver-specific match section to raise ipheth route metrics above Wi‑Fi. |
install/config/hardware/network.sh |
Installs the new NetworkManager drop-in on fresh installs. |
migrations/1777042493.sh |
Migrates existing systems by copying the drop-in into /etc and reloading NetworkManager. |
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Plugging an iPhone into USB (even just to charge) loads the ipheth kernel driver, which exposes the phone as a generic USB ethernet device. It then matches /etc/systemd/network/20-ethernet.network (which catches eth*/en*) and gets RouteMetric=100 — beating Wi-Fi at 600 and taking over the default route the moment the phone hands out a DHCP lease. This often breaks connectivity when the phone has no data plan, poor signal, or tethering disabled upstream. Add 15-ipheth.network with [Match] Driver=ipheth and RouteMetric=700. systemd-networkd processes .network files in lexical order and uses the first match, so iPhone interfaces hit this file before the generic ethernet one. Wi-Fi (600) now wins when both are up; if Wi-Fi drops, the tether still takes over automatically. Install on fresh systems via install/config/hardware/network.sh, and migrate existing systems via a new migration that also reloads systemd-networkd.
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Sorry about this one, Claude hallucinated and created a branch and a PR without being asked to. |
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Summary
Plugging an iPhone into USB (even just to charge) loads the
iphethkernel driver, which exposes the phone as a generic USB ethernet device. It then matches/etc/systemd/network/20-ethernet.network(which catcheseth*/en*) and getsRouteMetric=100— beating Wi-Fi at 600 and taking over the default route the moment the phone hands out a DHCP lease. Users lose internet when simply charging their phone if the tether can't actually reach the internet (no data plan, poor signal, tethering disabled upstream).This PR adds
/etc/systemd/network/15-ipheth.networkwith[Match] Driver=iphethandRouteMetric=700. systemd-networkd processes.networkfiles in lexical order and uses the first match, so iPhone interfaces hit this file before the generic20-ethernet.network. Wi-Fi (600) now wins when both are up; if Wi-Fi drops, the tether still takes over automatically. Real USB ethernet dongles use different drivers (CDC-ECM/NCM/RNDIS) and are unaffected.Changes
default/systemd/network/15-ipheth.network— the drop-in (Driver=ipheth, metric 700,RequiredForOnline=noso boot never waits on the phone).install/config/hardware/network.sh— installs the drop-in on fresh systems.migrations/1777042493.sh— installs the drop-in on existing systems and reloads systemd-networkd.Why driver-based matching
iphethis a Linux kernel driver specific to Apple's iPhone USB tethering protocol (vendor05ac, iPhone product IDs). It doesn't bind to iPads, Android phones, or generic USB-ethernet adapters, soDriver=iphethis a perfect filter for "this interface came from an iPhone."Test plan
eth0appears → default route moves to172.20.10.1at metric 100 → Wi-Fi deprioritized → internet breaks when tether has no upstream.ip routeshowsdefault via 192.168.1.1 dev wlan0 ... metric 600before the iPhone route at metric 700./etc/systemd/network/15-ipheth.networkis in place andnetworkctl reloadsucceeds.🤖 Generated with Claude Code