Reverse USB Tethering

I decided to give reverse usb tethering a shot. I don't know which devices easily support this, but I assume you have to be root. In my particular case, I was using an ICS device.  These steps could easily screw up your existing cell routing - so make sure your willing to risk it.

Step 0: Make sure the device is booted and connected via USB

Step 1: Enable tethering on the device side

• Go to Settings
• Under the Wireless & Networks, click on More
• Click on Tethering & portable hotspot
• Enable USB Tethering

Step 2: Get the IP Address of the device

malachi@onyx:~$ adb shell
root@android:/ # netcfg
lo       UP                                   127.0.0.1/8   0x00000049 00:00:00:00:00:00
dummy0   DOWN                                   0.0.0.0/0   0x00000082 62:bc:02:e1:d5:ea
rmnet0   DOWN                                   0.0.0.0/0   0x00000000 00:00:00:00:00:00
rmnet1   DOWN                                   0.0.0.0/0   0x00000000 00:00:00:00:00:00
rmnet2   DOWN                                   0.0.0.0/0   0x00000000 00:00:00:00:00:00
rmnet3   DOWN                                   0.0.0.0/0   0x00000000 00:00:00:00:00:00
rmnet4   DOWN                                   0.0.0.0/0   0x00000000 00:00:00:00:00:00
rmnet5   DOWN                                   0.0.0.0/0   0x00000000 00:00:00:00:00:00
rmnet6   DOWN                                   0.0.0.0/0   0x00000000 00:00:00:00:00:00
rmnet7   DOWN                                   0.0.0.0/0   0x00000000 00:00:00:00:00:00
sit0     DOWN                                   0.0.0.0/0   0x00000080 00:00:00:00:00:00
rndis0   UP                              192.168.42.129/24  0x00001043 da:02:11:22:14:af

Step 3: Get the matching IP Address of the workstation

malachi@onyx:~$ ifconfig -a usb0
usb0      Link encap:Ethernet  HWaddr e2:31:b5:d7:f3:7b 
          inet addr:192.168.42.74  Bcast:192.168.42.255  Mask:255.255.255.0
          inet6 addr: fe80::e031:b5ff:fed7:f37b/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1990 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1188 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:181334 (181.3 KB)  TX bytes:657452 (657.4 KB)

Step 4: Ping the device from the workstation

malachi@onyx:~$ ping 192.168.42.129
PING 192.168.42.129 (192.168.42.129) 56(84) bytes of data.
64 bytes from 192.168.42.129: icmp_req=1 ttl=64 time=1.01 ms
64 bytes from 192.168.42.129: icmp_req=2 ttl=64 time=0.605 ms

Step 5: Ping the workstation from the device

root@android:/ # ping 192.168.42.74
PING 192.168.42.74 (192.168.42.74) 56(84) bytes of data.
64 bytes from 192.168.42.74: icmp_seq=1 ttl=64 time=0.427 ms
64 bytes from 192.168.42.74: icmp_seq=2 ttl=64 time=0.397 ms

Step 6: Add workstation as the default gateway for the device

root@android:/ # route add default gw 192.168.42.74 dev rndis0

Step 7: Get a list of DNS servers from the workstation

malachi@onyx:~$ cat /etc/resolv.conf
nameserver 172.29.224.11
nameserver 8.8.8.8

Step 8: Add them to the device

root@android:/ # setprop net.dns1 172.29.224.11
root@android:/ # setprop net.dns2 8.8.8.8

Step 9: Setup forwarding from usb0 to eth1 on the workstation
[ most people probably use eth0. Just use ifconfig to check which one is active]

malachi@onyx:~$ sudo su - root
[sudo] password for malachi:
root@onyx:~# echo 1 > /proc/sys/net/ipv4/ip_forward
root@onyx:~# exit

malachi@onyx:~$ sudo iptables --flush -t nat
malachi@onyx:~$ sudo iptables --table nat --append POSTROUTING --out-interface eth1 -j MASQUERADE
malachi@onyx:~$ sudo iptables --append FORWARD --in-interface usb0 -j ACCEPT

Step 10: ping google ;)

malachi@onyx:~$ adb shell
root@android:/ # ping google.com
PING google.com (74.125.127.99) 56(84) bytes of data.
64 bytes from pz-in-f99.1e100.net (74.125.127.99): icmp_seq=1 ttl=51 time=11.8 ms
64 bytes from pz-in-f99.1e100.net (74.125.127.99): icmp_seq=2 ttl=51 time=11.9 ms

And finally, check things like the Browser...