RPI-Wireless-Hotspot

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Revision as of 15:20, 10 November 2012 by Bredman (Talk | contribs)

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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.

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 udhcpd

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

 start 192.168.2.2 # This is the range of IPs that the hostspot will give to client devices.
 end 192.168.2.20
 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 192.168.2.1 # 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 192.168.2.1

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 192.168.2.1
   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:

 wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
 iface default inet dhcp

to:

 #wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
 #iface default inet dhcp

3. Configure HostAPD. Edit the file /etc/hostapd/hostapd.conf (create it if it doesn't exist) and add the following lines:

 interface=wlan0
 ssid=Your Network Name Here
 hw_mode=g
 channel=6 # Change this channel to one of your choosing, between 1 and 12. If you have connection issues, try changing the channel.
 auth_algs=1 # This will create an open, unencrypted WiFi network. Use at your own risk.
 wmm_enabled=0 # Some wireless adapters/drivers have issues with 802.11n, this disables it (basically).

Change ssid= and channel= 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. For many, many more options see the file /usr/share/doc/hostapd/examples/hostapd.conf.gz

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

 #DAEMON_CONF=""

to:

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

4. Configure NAT. NAT (Network Address Translation) 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 if fairly easy to set up. First, edit the file /etc/sysctl.conf and add the following line to the bottom of the file:

 net.ipv4.ip_forward=1

This will enable NAT in the kernel. Second, 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.