Android USB tethering

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This article has some todo items:
  • make section USB tethering more generic
  • do NOT add Bluetooth tethering
  • verify HW list

Tethering, or phone-as-modem (PAM) is the sharing of a mobile device's Internet connection with other connected computers. Connection of a mobile device with other devices can be done over wireless LAN (Wi-Fi), over Bluetooth or by physical connection using a cable, for example through USB. The focus of this article is USB tethering with Android devices.

Android mobile phones can behave as an external network interface usbN, connected via the USB infrastructure. The usbN interface is in turn connected to the mobile phone LAN, providing DHCP server, DNS server, and a gateway.

That is how a mobile phone can provide an Internet connection to another device.

Android phones are already equipped to provide this functionality. Simply connect the USB cable and go to Settings -> Wireless settings -> Tethering -> Tethering USB.

What you need is some kernel and network configuration on the other side (e.g. a laptop).

Kernel

Selected kernel modules can either be built-in build as loadable linux kernel modules.

KERNEL Required kernel options
Device Drivers --->
    [*] Network device support --->
        <M> USB Network Adapters --->
            <M> Multi-purpose USB Networking Framework
                <M>  CDC Ethernet support (smart devices such as cable modems)
                <M>  CDC EEM support
		<M>  Host for RNDIS and ActiveSync devices
                <M>  Simple USB Network Links (CDC Ethernet subset)
                     [*] Embedded ARM Linux links (iPaq, ...)
    [*] USB support  --->
        <M> USB Modem (CDC ACM) support
        <M> USB Wireless Device Management support
        <M> USB Gadget Support  ---->
                USB Gadget precomposed configurations --->
                    <M> Ethernet Gadget (with CDC Ethernet support)
                    [*]   RNDIS support
                    [*]   Ethernet Emulation Model (EEM) support
                    <M> Network Control Model (NCM) support
Important
RNDIS linux module is being deprecated and will be removed from the Linux Kernel in favor Network Control Model (NCM), but it is used by majority of devices nowadays (2023) and up to now the only way to configure working USB tethering for old Android devices.[1] For more recent devices (Android 14 era) try to use "Network Control Model (NCM) support" module first.

For configuration check this thread and here.

Testing

After connecting a android device following events appear in the dmesg:

user $dmesg
usb 1-7: New USB device found, idVendor=18d1, idProduct=4e13
usb 1-7: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-7: Product: Nexus One
usb 1-7: Manufacturer: Google, Inc.
usb 1-7: SerialNumber: HT9CSP803294
usb 1-7: usb_probe_device
usb 1-7: configuration #1 chosen from 1 choice
usb 1-7: adding 1-7:1.0 (config #1, interface 0)
rndis_host 1-7:1.0: usb_probe_interface
rndis_host 1-7:1.0: usb_probe_interface - got id
rndis_host 1-7:1.0: usb0: register 'rndis_host' at usb-0000:00:1d.7-7, RNDIS device, ea:61:37:88:a2:e5
usb 1-7: adding 1-7:1.1 (config #1, interface 1)
drivers/usb/core/inode.c: creating file '004'
hub 1-0:1.0: state 7 ports 8 chg 0000 evt fe80
uhci_hcd 0000:00:1d.0: reserve dev 2 ep81-INT, period 8, phase 4, 93 us
usb 1-7: link qh32-0001/ffff88021aa4bc80 start 1 [1/0 us]
usb0: no IPv6 routers present
user $ip link

If you see usbN interface (N may be a different number) you are all set.

Connecting

Since the mobile phone LAN changes its addresses, you need a DHCP client to configure the usbN device.

If you are on a laptop, you probably have a DHCP client. If not, emerge net-misc/dhcpcd:

root #emerge --ask net-misc/dhcpcd

Manually

Simply run dhcpcd after plug/mobile activation:

root #dhcpcd usb0

Permanent configuration

Edit your /etc/conf.d/net to have a permanent, automatic activation of the interface.

FILE /etc/conf.d/net
# ...
config_usb0="dhcp"
# ...

Once plugged in and activated on the mobile phone side, the usb0 will be up and configured.

Checks

Run the usual checks to verify the connection:

root #ip link show usb0
root #ip route
root #cat /etc/resolv.conf

Advanced network settings

DHCP is very quick, but the default settings don't give you as much freedom as you may want.

A possible scenario is that you are in a corporate, protected LAN context that doesn't provide Internet connection but you need to stay connected to have access to some Intranet resource or you have a free but limited connection (a public WiFi network allowing HTTP only, an evil firewall, etc.). Since mobile connections could be expensive, you could want to save money by tethering only when needed.

Here is a handful of examples pertaining to DHCP usage.

If you want to limit the information set by DHCP, you can fine-tune its behavior:

root #dhcpcd --nogateway --nohook resolv.conf --nohook hostname usb0

This will let your default gateway, resolv.conf and hostname as they are, letting you provide extra info by hand:

root #ip route add my_sshd_remote_host_IP scope host dev usb0

Finally, you can permanently configure your USB network interface:

FILE /etc/conf.d/net
config_usb0="dhcp"
dhcpcd_usb0="--nogateway --nohook resolv.conf --nohook hostname"
# Special hosts
postup()
{
    if [[ "usb0" == ${IFACE} ]]; then
        ip route add my_sshd_remote_host_IP scope host dev usb0
    fi
}

Generally, you can avoid every DHCP setting but gather them with:

root #dhcpcd -U usb0

Then you can set what you want in the postup hook.

Tested devices

Tested devices list.

Device OS Notes
Fairphone 2 Fairphone OS Android 6.0.1, build no FP2-gms-18.04.1 rndis_host required
Google Nexus One Android 2.3.6 build GRK39F
Google Nexus 4 Android 4.3 build JWR66Y rndis_host required
Google Pixel 3 Android 12 rndis_host required
HTC Desire HD Android 2.3.6 Stock Rom build and Android 4.4.4 (unofficial CyanogenMod 11) rndis_host required
HTC One M7 Sense 5.5, Android 4.3, Software number 3.62.401.1,HTC SDK API level 5.65 rndis_host, cdc_ether and usbnet modules ONLY to get it to work
Huawei Honor 4x unofficial CyanogenMod 11 / Android 4.4.4 rndis_host required
Huawei Honor View 10 Lite Model JSN-10L, Android 10 autoloads rndis_host, cdc_ether and usbnet modules; it works flawlessly
Huawei P10 Android 8.0.0 stock
LG P350 Android 2.2.1 build FRG83
LG E400 Android 2.3.6 build GRK39F
LG L7 P705 Android 4.1.2 build JZO54K
Motorola Defy Android 2.3.7 Cyanogenmod 7
Motorola Moto G 4G 2013 (1st Gen) Android 5.1 rndis_host required
OnePlus One rndis_host required
OnePlus 3T rndis_host required
PINE64 PinePhone (pine64-pinephone postmarketOS GNU/Linux 5.17.0-rc8 non Android based phone rndis_host required
Samsung Galaxy Grand Neo+ Duos GT-I9060I / Android 4.4.4 only needed rndis_host - cdc_ether - usbnet modules
Samsung Galaxy Nexus i9250 Android 4.0.1 ITL41D, Android 6.0.1 (CyanogenMod 13) rndis_host required
Samsung Galaxy S i9000
Samsung Galaxy S2
Samsung Galaxy S3 GT-I9300 Android 4.3 Stock Rom
Samsung Galaxy S4 Mini Duos GT-I9192, unofficial CyanogenMod 12.1 / Android 5.1 rndis_host required
Samsung Galaxy S5 Android 6.0.1 rndis_host required
Samsung Galaxy S6 Android 7.0 rndis_host required
Samsung Galaxy S7 rndis_host required
Samsung Galaxy Tab 2 7.0 Android 4.1.2
Sony Xperia Go St27i Android 4.1.2 Stock Rom build no 6.2.A.1.100 rndis_host required
Sony Xperia X Compact Android 8.0.0, build no 34.4.A.2.118 needed rndis_host module and "Embedded ARM Linux links" (CONFIG_USB_ARMLINUX) on kernel 4.16.18
Sony Xperia XZ Premium G8142 Stock Android 8.0, build no 47.1.A.8.49 rndis_host required
Wileyfox Storm CyanogenOS 13.1.5 - Android 6.0.1
Xiaomi Redmi 5 MIUI 9, 10 and 11

See also

References

  1. ↑ https://lkml.org/lkml/2022/11/23/1502
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