README.md

Make a Pi into a RoboRouter

With this project we try to tackle the problem that most comercially available toy robots create their own WiFi networks. But in order to connect these robots to the cloud and control them over the internet we need to be able to connect them to an existing network with internet access. We cannot make the robot connect to another network, thus we use a Raspberry Pi to create a network bridge. The Pi connects via a WiFi dongle to the robot's network, and uses it's ethernet to connect to the network with internet access. It then forwards all traffic coming in on a given port to the robot. The User can connect to the Pi as if it was the robot and all traffic is forwarded from/to the robot.

Neccessary Hardware:

1. Pi
2. WiFi Dongle (to connect to the robot)
3. Ethernet Cable (to connect to your home network)

Note: You need one RoboRouter per Robot because each robot is making it's own wifi network, and it is not possible to switch wifi networks fast enough to have a concurrent communication with robots on different networks.

Define networks

Copy over the file /etc/wpa_supplicant/wpa_roam.conf

To add a new robot network

Add the following template to wpa_roam.conf

    network={
        ssid="<NETWORK_SSID>"
        key_mgmt=NONE
        id_str="<UNIQUE_ID>"
    }

replace <NETWORK_SSID> with the network id (SSID) of the robot and replace <UNIQUE_ID> with an identification string of your choice. This string will be used to reference the robot in the interfaces definition and should be unique.

Use

    $ iwlist wlan0 scan

to get the network information. If it says Mode:Ad-Hoc, the robot is using an AdHoc network and you have to add

    mode=1
    frequency=<FREQUENCY>

to the above network definition template. Replace <FREQUENCY> with the frequency specified in the iwlist scan result.

Setup the network interfaces

Copy over the file /etc/network/interfaces

To add a new robot

1. We need to know the IP address of the robot and the ports on which the robot communicates. If you have that ready, go to step 2, otherwise use nmap to check the network for hosts and scan thoses hosts for open ports:

   e.g. if the robot is on the subnet 192.168.1

        $ nmap -n 192.168.1.0/24 -e wlan0

   which gives a result of the format:

        Nmap scan report for 192.168.1.100
        Host is up (0.037s latency).
        Not shown: 999 closed ports
        PORT   STATE SERVICE
        80/tcp open  http

2. If the robot has a different subnet than your home network, e.g. your robot is on the subnet 192.168.0 and your home network on 192.168.1, add the following template to the interfaces file:

        iface <UNIQUE_ID> inet dhcp
          # forward all packages coming in on the given port to the robot's
          # ip address and port. the two <PORT_NR> can be the same or different.
          # add one entry per port that the robot uses
          up iptables -t nat -A PREROUTING -i eth0 -p tcp --dport <PORT_NR> -j DNAT --to-destination <ROBOT_IP>:<PORT_NR>

   replace: <UNIQUE_ID> with the identification string defined earlier <ROBOT_IP> with the ip of the robot <PORT_NR> with the port number that the robot uses

3. If the robot has the same subnet, add this part to the above template;

        # this will make all packages with the given firewall mark to
        # go through the wlan0 interface
        up ip route flush table <TABLE_ID>
        up ip rule add fwmark <FWMARK_ID> table <TABLE_ID>
        up ip route add default dev wlan0 table <TABLE_ID>
        up ip route flush cache
        #up sysctl net.ipv4.conf.wlan0.rp_filter=0
        
        # set the firewall mark for all packages coming in on the given port
        # add one entry per port that the robot uses
        up iptables -A PREROUTING -i eth0 -t mangle -p tcp --dport <PORT_NR> -j MARK --set-mark <TABLE_ID>

   replace: <TABLE_ID> with a number of your choice <FWMARK_ID> with a number of your choice, can be the same or different than the <TABLE_ID> <PORT_NR> with the same port number used for the entry in the above template

Manage RoboRouter to switch between robots

Only one robot can be connected at a time. To make the pi switch from one robot to another, use the command line tool wpa_cli

1. Select network

        $ wpa_cli select_network <NETWORK_ID>

   e.g.

        $ wpa_cli select_network 1
        Selected interface 'wlan0'
        OK

2. List defined networks

        $ wpa_cli list_networks

   e.g.

        $ wpa_cli list_networks
        Selected interface 'wlan0'
        network id / ssid / bssid / flags
        0	Rover_00E04C07F81A	any	
        1	AC13_00E04C06E710	any	
        2	HC00FF83	any	

3. Get network status

        $ wpa_cli status

   e.g.

        $ wpa_cli status
        Selected interface 'wlan0'
        bssid=80:07:a2:00:ff:83
        ssid=HC00FF83
        id=2
        id_str=spytank
        mode=station
        pairwise_cipher=NONE
        group_cipher=NONE
        key_mgmt=NONE
        wpa_state=COMPLETED
        ip_address=10.10.1.100
        address=24:3c:20:08:9d:48

Find the RoboRouter on the Network

In order to use the RoboRouter we need to know it's ip address. If you don't want to put a screen on the Pi, or check the router, you can either set a static ip address or use the following easy setup:

1. install xinetd

        $ sudo apt-get install xinetd

2. open the files /etc/xinetd.d/time and /etc/xinet.d/echo and change to disable = false

3. now you can use nmap on another computer to scan the network and check which hosts have the ports 7 and 37 open. This will be the robot router. (It is not guaranteed that no other computer has these ports open, but it's highly unlikely, as they are rarely used)

   e.g.

        $ nmap -Pn -p7,37 <IP_ADDRESS>/24 -oG - | awk '/open/{print "  " $2}'

   replace <IP_ADDRESS> with the ip address of the computer.