How-To: Turn a Raspberry Pi into a WiFi router

Do you want a separate WiFi network for your guests? or would you like to have network running an alternative DNS configuration in your house? You no longer have to buy a new WiFi router to do this – you can turn your Raspberry Pi into a WiFi router.

This post will guide you through the process of setting up your Raspberry Pi as a WiFi network.

Prerequisites & Equipment

You are going to need the following:

• A Raspberry Pi (Buy here)
• A USB WiFi Adapter (I use the Edimax USB adapter – its small and cheap!)
• A SD Card flashed with the Raspbian OS (Here is a guide if you need)
• Access to the Raspberry either via keyboard and a monitor or remotely

Raspberry Pi with Edimax Wifi Adapter

Before we proceed I want to point out the importance of buying the right USB WiFi Adapter. As you may have experienced with other types of hardware devices not all devices are plug-n-play. Sometimes you will need to download a driver to make them work. While drivers are normally readily available for Windows computers – it is a different world for Linux and Raspberry Pi’s. This is why it is very important to buy a WiFi Adapter that mentions “Linux” in the product description or package. I use the Edimax – Wireless USB adapter because I have found it to be cheap and very easy to work with. I very recommend you do the same – it could save you a lot of headaches.

Getting WiFi adapter running on the Raspberry Pi

Plug the USB WiFi adapter into one of the free USB ports on the Raspberry Pi. Power up the Raspberry Pi. At this point you need to either connect to the Raspberry Pi via an Ethernet cable or use a keyboard and a monitor to access the Raspberry Pi.

If you need help connecting to the Raspberry Pi look at this post remotely using a wired network connection.

After booting and logging-in you want to make sure that the Raspberry Pi found your new wireless adapter. To look at which peripherals the operating system found when booting run the following command:

dmesg | more

You can use the spacebar to scroll down a page at a time – towards the end you will see something similar to the following lines:

[ 3.282651] usb 1-1.2: new high-speed USB device number 4 using dwc_otg
[ 3.394810] usb 1-1.2: New USB device found, idVendor=7392, idProduct=7811
[ 3.407489] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 3.420530] usb 1-1.2: Product: 802.11n WLAN Adapter

This means that the operating system recognized the USB WiFi Adapter using one of the built-in drivers (you can return to the terminal by pressing “q”). All that is left is to configure your WiFi connection.

Install the router software

In order for the Raspberry Pi to act as a WiFi router and access point you need to install some extra software on the Raspberry. You are going to need the following pieces of software:

• hostapd
  HostAPD is a user space daemon for access point and authentication servers. That means it can will turn your Raspberry Pi into a access point that other computers can connect to. It will also handle security such that you can setup a WiFi password.
• isc-dhcp-server
  isc-dhcp-server is the Internet Systems Consortium’s implementation of a DHCP server. A DHCP server is responsible for assigning addresses to computers and devices connection to the WiFi access point.

To install the DHCP software run the following command:

sudo apt-get install isc-dhcp-server

Next up is the HostAPD software. Because our USB stick needs an access point driver not supported by the native HostAPD application we must install a custom version compiled with the driver we need. This can be done by running the following commands one at a time.

wget https://github.com/jenssegers/RTL8188-hostapd/archive/v1.1.tar.gz
tar -zxvf v1.1.tar.gz
cd RTL8188-hostapd-1.1/hostapd sudo make sudo make install

This will take a little time – while waiting for the program to compile send a friendly thought to Jens Segers over at http://jenssegers.be for making this software available.

Once downloaded we are ready to configure the software.

Configure the ISC-DHCP-Server

To configure the DHCP server open the file /etc/dhcp/dhcpd.conf in your favorite text editor. You can open it in nano using this command:

sudo nano /etc/dhcp/dhcpd.conf

Find the following section and comment it out by placing a hashtag at the beginning of the line.

option domain-name "example.org";
option domain-name-servers ns1.example.org, ns2.example.org;

Next find the section below and un-comment the word authoritative (remove hastag):

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
#authoritative;

The file now looks like this:

Next we need to define the network and network addresses that the DHCP server will be serving. This is done by adding the following block of configuration to the end of file:

subnet 192.168.10.0 netmask 255.255.255.0 {
 range 192.168.10.10 192.168.10.20;
 option broadcast-address 192.168.10.255;
 option routers 192.168.10.1;
 default-lease-time 600;
 max-lease-time 7200;
 option domain-name "local-network";
 option domain-name-servers 8.8.8.8, 8.8.4.4;
}

This will enable the DHCP server to hand out the ip addresses from 192.168.10.10 to 192.168.10.20 in its own local network. People who are skilled in network configuration can change these values if they wish to use some other network addresses and/or other DNS servers. This configuration will use the Google DNS servers at 8.8.8.8 and 8.8.4.4. 

To save the file press Ctrl+O this will write the file to the disk – afterwards you can exit nano by pressing Ctrl+X. If nano asks if you want to Save modified buffer? press “Y” followed by hitting enter to confirm the filename.

Next file to edit is /etc/default/isc-dhcp-server, you can open it in nano using this command:

sudo nano /etc/default/isc-dhcp-server

Scroll down to the line saying interfaces and update the line to say:

INTERFACES="wlan0"

This will make the DHCP server hand out network addresses on the wireless interface. Save the file and exit nano.

The last step in configuring the DHCP server is to configure a static ip address for the wireless network adapter. This is done in the file /etc/network/interfaces – before opening it make sure the WLAN interface is down. Do this with the following commands:

sudo ifdown wlan0
sudo nano /etc/network/interfaces

Change the file to look like this:

This will make the wireless adapter take the address 192.168.10.1 in our new local network. Remember to comment out the last 3 lines of the file.

This concludes the setup of the DHCP server – however we still cannot connect to our new network because we have not setup the access point yet. This is done by configuring the hostapd application. 

Configuring HostAPD

To configure HostAPD, open the file called /etc/hostapd/hostapd.conf in your favorite text editor. You can open it in nano using this command:

sudo nano /etc/hostapd/hostapd.conf

The standard configuration will create a new wireless network called wifi with the password YourPassPhrase. You can change the parameter “ssid=wifi” to the SSID wifi name you want and the parameter “wpa_passphrase=YourPassPhrase” to your own password.

This concludes the configuration of our access point software HostAPD. Next up is enabling NAT.

Enable NAT

The last step before we can start the access point is setting up Network Address Translation (NAT). This will make sure that our network traffic will be able to reach the internet using the Raspberry Pi’s Ethernet cable connection to your internet router.

Open /etc/sysctl.conf with:

sudo nano /etc/sysctl.conf

Scroll down to the last line of the file and add the line:

net.ipv4.ip_forward=1

Next start the translation right away by running:

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

Start the wireless network by running:

sudo ifup wlan0

Next step is setting up the actual translation between the ethernet port called eth0 and the wireless card called wlan0.

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

With the NAT configured it is now time to run your access point for the first time.

Starting your wireless router

You are now ready to start the DHCP server and the HostAPD access point application.You can do so by running:

sudo service isc-dhcp-server start
sudo service hostapd start

At this point you should be able to find your wireless network on your laptop and connect to it and the internet!

Finishing up …

While it is pretty cool you now have your Raspberry Pi running as a wireless access point it is not so cool you have to login every time it reboots to start the HostAPD and DHCP software…

To avoid this run the following commands:

sudo update-rc.d hostapd enable 
sudo update-rc.d isc-dhcp-server enable

To avoid having to configure NAT every time the Raspberry Pi reboots you can do the following.

Run this command to backup the NAT configuration.

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

Add the following to the end of the file /etc/network/interfaces to restore the configuration when the network interface comes up:

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

The file should now look like:

At this point try to reboot the raspberry pi just to make sure everything works as intended – you can reboot with the command:

sudo reboot

Hopefully you will see your new access point come online again. After it comes up again you should be able to connect to it and access the internet!