The BiT Bang Theory

Hi! Following my latest posts on how to get started with the Raspberry Pi "headless mode" and Using Bluetooth with the Raspberry Pi now I'll show how to turn the Raspberry Pi into a Wireless Access Point. Most of this post follows what is described here but I added a few more steps. Moreover, I ran into some troubles and had to do some troubleshooting. I used a D-Link DWA-140 Rangebooster N Adapter which contains a Ralink RT2870 chipset.

(Click the photo for better resolution in Picasa Photostream)

The process looks a little long but it can be done in under 10 minutes :) . Every time you need to edit or create some file (for example /etc/udhcpd.conf) among this process you can use "sudo nano /etc/udhcpd.conf".

So, first thing to do is to check if the dongle is being properly recognized. Open the terminal and type:

lsusb

and if it is being recognized you should see something regarding a wireless adapter. Mine says:

Bus 001 Device 005: ID 07d1:3c09 D-Link System DWA-140 RangeBooster N Adapter(rev.B1) [Ralink RT2870]

Now you'll have to instal the "iw" tool to see which modes are supported by your wireless dongle. Open the terminal and type:
```
sudo apt-get install iw
```
After it finishes installing enter the following command:
```
iw list
```
Then you should see lots of specs being printed and somewhere in the middle you should find something like this (the modes below are the ones supported by the USB dongle that I'm using):
```
Supported interface modes:
   * IBSS
   * managed
   * AP
   * AP/VLAN
   * WDS
   * monitor
   * mesh point
```
If there is the AP option then you can keep going. Otherwise that mode is not supported by your wireless dongle and you should get a different one.
The next step will be to install "hostapd" and "udhcpd":
```
sudo apt-get install hostapd udhcpd
```

Now let's configure DHCP so that the Raspberry Pi will be able to hand out IP addresses to the clients. Edit the file /etc/udhcpd.conf to contain the following:

start 192.168.42.2 # This is the range of IPs that the hostspot will give to client devices.
end 192.168.42.20
interface wlan0 # The device uDHCP listens on.
remaining yes
opt dns 8.8.8.8 4.2.2.2 # The DNS servers client devices will use.
opt subnet 255.255.255.0
opt router 192.168.42.1 # The Pi's IP address on wlan0 which we will set up shortly.
opt lease 864000 # 10 day DHCP lease time in seconds

The next step is to edit the file /etc/default/udchpd and change the line
```
DHCPD_ENABLED="no"
```
to
```
#DHCPD_ENABLED="no"
```
Now let's give the Pi a static IP address by entering the following command:
```
sudo ifconfig wlan0 192.168.42.1
```
To set this up automatically we must edit the file /etc/network/interfaces and replace the line "iface wlan0 inet dhcp" to:
```
iface wlan0 inet static
  address 192.168.42.1
  netmask 255.255.255.0
```
If the line "iface wlan0 inet dhcp" does not exist, add the referred lines at the bottom of the file. You will also have to change the lines (they may not be next to each other)
```
allow-hotplug wlan0
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet manual
```
to
```
#allow-hotplug wlan0
#wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
#iface default inet dhcp
```
Now we'll need to configure hostapd, which is used to create the network. The network may be an open network or a WPA-secured network for authorised access only. To do that we'll have to create some files and edit others. The first file that we'll need to edit/create is "/etc/hostapd/hostapd.conf". For a WPA-secured network make it look like this:
```
interface=wlan0
driver=nl80211
ssid=My_AP
hw_mode=g
channel=6
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=My_Passphrase
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP
```
You can change the SSID, channel and wpa_passphrase to whatever you want. SSID is the name of the hotspot and the wpa_passphrase is the password that will be required to access the network. The channel is used to select the operating frequency of the wireless access point. In case you have another AP or router at home, make sure that you choose a free channel so that they won't interfere with each other. If you prefer to create an open network just enter the following text in the file instead:
```
interface=wlan0
ssid=My_AP
hw_mode=g
channel=6
auth_algs=1
wmm_enabled=0
```
Now we'll have to change a variable inside the file /etc/default/hostapd so that it points to the file that we have just created/edited. Change this line:
```
#DAEMON_CONF=""
```
to
```
DAEMON_CONF="/etc/hostapd/hostapd.conf"
```
The next thing to do is to configure NAT (Network Address Translation) which is a technique that allows several devices to use a single connection to the internet. Edit the file /etc/sysctl.conf and add the following line to the end of the file:
```
net.ipv4.ip_forward=1
```
It will enable NAT in the kernel. Now, run the following commands:
```
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT
```
And this concludes the NAT configuration. To make it permanent so you don't have to run the commands after each reboot, run the command
```
sudo sh -c "iptables-save > /etc/iptables.ipv4.nat"
```
and edit the file /etc/network/interfaces and add the following lines to the end of the file:
```
up iptables-restore < /etc/iptables.ipv4.nat
```
We're almost finishing! Now it's time to get it running! Run the following commands to start the Access Point:
```
sudo service hostapd start
sudo service udhcpd start
```
And your Pi should finally be hosting a wireless hotspot! :) To get it to start on boot everytime, run these two last commands:
```
sudo update-rc.d hostapd enable
sudo update-rc.d udhcpd enable
```

And you're done! If you followed every step correctly everything should be working as expected... Unless you're familiar to the Laws of Murphy (like me :P) and nothing can just work at first time! Everytime I turned on the Raspberry Pi I could see the wireless network appearing but with a very week signal and after less then a minute it would be gone. Strange thing, huh? So I tried to restart hostapd to see if it would reappear but nothing would happen. The only way to bring the wireless network to life again was by rebooting the Pi. I checked if Rasbpian Wheezy came with some kind of network manager that could be messing with the wireless dongle but once again I couldn't find the problem. Then I remembered that it could be a power issue! When it would show the signal was very low and the fact that nothing would bring it to life except by cutting and restoring power to the Raspberry Pi could indicate some sort of hardware malfunction. Another fact that could make my hypothesis to be true was the 140mA current limit on each USB port of the Raspberry Pi. 140mA may not be enough to power some USB Wi-Fi dongles and other devices. So I picked the USB Hub that I had previously modified to allow an external power source and connected everything to it, including the Pi. Turned the 5V, 1A power supply on and voilá! Everything was finally working as expected! In fact, this whole post has been written using the Raspberry Pi as a Wireless Access Point. It has been turned on for a while now and keeps quite stable and fast. If you run into some problems you can also check the Rasperry Pi forum thread that originated this tutorial here. I hope this post was useful for you and that you enjoyed reading it.

Take care! :)

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