RPI-Wireless-Hotspot

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What does it do?

This project configures your Raspberry Pi to connect to the Internet through ethernet, and share that connection over WiFi.

What do you need?

  • A Raspberry Pi, model B.
  • A boot SD card for the Raspberry Pi.
  • A USB WiFi device that supports "Access Point" mode.
  • An Ethernet cable to connect to the local network.

Determine wifi adapter chipset

Doing a Google search on the manufactures part number usually gets results e.g. "Cnet CWP-854 chipset" should give you the result of Ralink rt2561 or rt61. The other option is to plug the wifi adapter into a Linux box and type the commands:

sudo lspci

for PCI adapters

sudo lsusb

for USB adapters

sudo iwconfig

Using these commands you should have enough clues to your wifi adapters chipset.

Please make sure you Wifi dongle supports Access Point or Master Mode

  • Edimax does NOT support Access Point (UPDATE 7/9/13: Edimax DOES support Access point, tutorial here: Raspberry Hotspot with Edimax USB WiFi Adapter)
  • AirLink 101 / AWL5088 does NOT support Access Point
  • Ralink RT5370 and RT5372 DO support Access Point


Test an adapter for "master mode"

To check if an adapter and driver can do master mode you can use a program called 'iwconfig'

sudo iwconfig

In the terminal window should list all available wireless interfaces. Assuming your adapter is connected and its drivers are loaded, try the following.

sudo iwconfig wlan1 mode master

Replace wlan1 with whatever Ubuntu is calling your adapter. If you don’t get an error you’re in business.

mac80211 based driver

Many newer drivers use the mac80211 framework. The iwconfig method of checking for master mode doesn't work with these drivers, because they use the new nl80211 interface for userspace communication.

You have to install 'iw' the new wireless configuring tool at first.

sudo aptitude install iw

'iw list' shows all supported features of all installed wireless card supporting the new nl80211 interface.

iw list

If there is 'AP' in the list of "Supported interface modes" your device will support the Access Point mode with hostapd.

...
Supported interface modes:
        * IBSS
        * managed
        * AP
        * AP/VLAN
        * monitor
        * mesh point
...

What skill level is required?

This project does not require any coding or compilation. Very basic Linux and networking knowledge would be useful, but not essential.

To edit a configuration file (for example /etc/udhcpd.conf) use the following command

sudo nano /etc/udhcpd.conf

You will find yourself in a simple editor. Move around using the arrow keys. To save the file press Ctrl-o. To exit press Ctrl-x.

How does it work?

The Raspberry Pi is configured as a WiFi Hotspot, just like you would see in an internet cafe. It allows you to connect to the internet over WiFi using the Raspberry Pi as the bridge to the internet. The basic steps are

  • Enable a WiFi Access Point and broadcast on the channel of your choice
  • Assign dynamic IP addresses to any device that connects to WiFi network
  • Join the WiFi and Ethernet networks together by using Network Address Translation

Instructions

The following steps were performed on Raspbian but should be much the same on any Debian-based distro.

1. Install the necessary software.

sudo apt-get install hostapd hostap-utils udhcpd bridge-utils

2. Configure DHCP. Edit the file /etc/udhcpd.conf and configure it like this:

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

Edit the file /etc/default/udhcpd and change the line:

DHCPD_ENABLED="no"

to

#DHCPD_ENABLED="no"

You will need to give the Pi a static IP address with the following command:

sudo ifconfig wlan0 192.168.42.1

To set this up automatically on boot, 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" is not present, add the above lines to the bottom of the file.

Change the lines (they probably won't all 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

3. Configure HostAPD. You can create an open network, or a WPA-secured network. A secure network is recommended to prevent unauthorized use and tampering, but you can also create an open network. To create a WPA-secured network, edit the file /etc/hostapd/hostapd.conf (create it if it doesn't exist) and add the following lines:

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

Change ssid=, channel=, and wpa_passphrase= to values of your choice. SSID is the hotspot's name which is broadcast to other devices, channel is what frequency the hotspot will run on, wpa_passphrase is the password for the wireless network. For many, many more options see the file /usr/share/doc/hostapd/examples/hostapd.conf.gz

If you would like to create an open network, put the following text into /etc/hostapd/hostapd.conf:

interface=wlan0
ssid=My_AP
hw_mode=g
channel=6
auth_algs=1
wmm_enabled=0

Change ssid= and channel= to values of your choice. Note that anyone will be able to connect to your network, which is generally not a good idea. Also, some regions will hold an access point's owner responsible for any traffic that passes though an open wireless network, regardless of who actually caused that traffic.

Edit the file /etc/default/hostapd and change the line:

#DAEMON_CONF=""

to:

DAEMON_CONF="/etc/hostapd/hostapd.conf"

4. Configure NAT (Network Address Translation). NAT is a technique that allows several devices to use a single connection to the internet. Linux supports NAT using Netfilter (also known as iptables) and is fairly easy to set up. First, enable IP forwarding in the kernel:

sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"

To set this up automatically on boot, edit the file /etc/sysctl.conf and add the following line to the bottom of the file:

net.ipv4.ip_forward=1

Second, to enable NAT in the kernel, 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

Your Pi is now NAT-ing. To make this permanent so you don't have to run the commands after each reboot, run the following command:

sudo sh -c "iptables-save > /etc/iptables.ipv4.nat"

Now edit the file /etc/network/interfaces and add the following line to the bottom of the file:

up iptables-restore < /etc/iptables.ipv4.nat

5. Fire it up! Run the following commands to start the access point:

sudo service hostapd start
sudo service udhcpd start

Your Pi should now be hosting a wireless hotspot. To get the hotspot to start on boot, run these additional commands:

sudo update-rc.d hostapd enable
sudo update-rc.d udhcpd enable

At the completion of these instructions, your Pi should be providing a wireless network and allowing other devices to connect to the Internet. From my experience, the Pi makes a decent access point, although with cheaper WiFi dongles range will be fairly limited. I haven't stress tested this setup, but it seems to work fairly well and is handy when a "real" access point isn't available. I wrote most of the instructions from memory, if you find any errors/typos I'll correct them.

This tutorial originally was a post on the Raspberry Pi forum here, you can reply to that topic if you have issues. Thanks go to all the people who tested my tutorial on the forum, and to poing who contributed the WPA HostAPD config.


Please make sure you Wifi dongle supports Access Point or Master Mode

  • Edimax doesn't support Access Point (UPDATE 7/9/13: Edimax DOES support Access point, tutorial here: Raspberry Hotspot with Edimax USB WiFi Adapter)
  • AirLink 101 / AWL5088 doesn't support Access Point
  • Ralink RT5370 supports Access Point