Reverse tethering of several Android devices via USB

Question

I'm trying to setup a testing environment for my android app where the separate devices need an Internet connection, but don't have wireless capabilities.

So I decided on using usb reverse tethering. My host machine is running Ubuntu. I already managed to setup reverse tethering for one device, the connection is working and I can ping google.com from this device's adb shell.

When I connect a second device, the first tethering stops working. Both devices have the same IP adress configured on their internal usb0 interface.

Here's what I have so far:

1. Port forwarding on host is activated

   echo 1 > /proc/sys/net/ipv4/ip_forward
   

2. Iptables rule on host to route traffic:

   iptables -t nat -A POSTROUTING -s 169.254.255.2/24 -j MASQUERADE
   

3. Plugin first device:

   ifconfig shows the device on usb0 @ ip 169.254.255.2/30
   

4. On first device (with adb shell)

   > route add default gw 169.254.255.2 dev usb0
   > setprop net.dns1 8.8.8.8
   > ping google.com --> is giving results
   

5. Plugin second device

   ifconfig shows this device on usb1 @ ip 169.254.255.2/30 
   

6. On second device

   Add gw, set DNS like above
   

Now the second device can ping google.com, but the first one not.

When I change the internal IP or the IPs assigned to the hosts usb0, usb1 interfaces I am not able to connect to the devices via adb anymore.

I suspect this to be a networking problem, rather than a problem with ADB? Any Ideas?

Answer 1

After a lot of googling and trial and error I finally found the solution for my particular setup.

What I did in the end, and what I missed in my first attempts, was to put each connected usb device into a separate subnet (see this answer on serverfault).

To put it clearly, the setup is now like following:

1. iptables contains the following rule

   iptables -t nat -A POSTROUTING -j MASQUERADE
   

2. the host's usb0 and usb1 interface, now in separate subnets

   usb0: inet addr:169.254.0.1  Bcast:169.254.15.255  Mask:255.255.240.0
   usb1: inet addr:169.254.16.1  Bcast:169.254.31.255  Mask:255.255.240.0
   

3. internal usb0 iface of Android device connected on host's usb0:

   - usb0 169.254.0.2/20
   - default gw 169.254.0.1 (so the host's usb0 iface)
   

4. internal usb0 iface of Android device connected on host's usb1:

   - usb0 169.254.16.2/20
   - default gw 169.254.16.1 (so the host's usb1 iface)
   

That way I now have Internet access (after adb shell setprop net.dns1 8.8.8.8) from each android device connected to the usb interfaces on my host.

Answer 2

You need a linux system with root access, rooted android phone and usb cable.

Steps

1. Install adb and fastboot in your linux system.

   sudo apt-get install android-tools-adb android-tools-fastboot

2. Connect your android phone to your PC via USB and enable USB tethering from the settings on your phone.
3. Open terminal in your PC and type the commands given below.

4. Find out the new network interface that was created on your PC.

   ifconfig

   Generally the new network interface will be usb0 or usb1. Let us consider usb0.

5. Now make some static IP address for this new interface usb0.

   sudo ifconfig usb0 10.42.0.1 netmask 255.255.255.0

6. Now make this new interface usb0 as shared connection.

   echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward

7. Now make some changes iptables firewall.

   sudo iptables -t nat -F sudo iptables -t nat -A POSTROUTING -j MASQUERADE

8. Now we have to enter some commands in the android phone. We can use either adb or directly typing the commands in the android phone through a terminal emulator installed in the phone. I am using the adb way.

9. Find the network interface in the android phone.

   adb shell busybox ifconfig

   Mine was rndis0.

10. Set the static IP, netmask and gateway.

    adb shell ifconfig rndis0 10.42.0.2 netmask 255.255.255.0 adb shell route add default gw 10.42.0.1 dev rndis0

11. Verify Internet connectivity on your phone.

    adb shell ping 8.8.8.8

    If it is pinging, then the Internet in your mobile is working.

This Internet connection will not work with the apps like opera mini and paytm, but works well with whatsapp.