Share WiFi With Ethernet Port on a Raspberry Pi

Do you have an old laser printer or scanner that still works great but isn't wifi compatible? Or maybe you want to connect an external hard drive as a backup device on your network and you've run out of ethernet ports on your home router. This instructable will help you create a bridge from the wifi connection to the ethernet port on a Raspberry Pi.

I needed a way to connect an older Xerox copier/printer that has a built in network adapter and network software but wasn't wifi compatible. This printer was in an older building and the printer was in a location that wasn't close to an ethernet punch down and couldn't be moved. With a few parts that I already had around my house I was able to put together a solution that solved my needs.

This easy DIY solution will give you the capability of adding a wifi connection to your older devices without breaking the bank by purchasing wireless print adapter.

1. Raspberry Pi (any model will do, but you'll see faster results with a model 3).
2. Power adapter for your Pi.
3. SD Card to install the operating system on (you could use an 8GB card up to whatever size you want. I usually go with a 32GB card in case I want to add more options to the RPi).
4. Wifi adapter
5. Ethernet cable
6. HDML cable (I have an old DVI monitor so I use this HDMI to DVI cable).
7. Keyboard and mouse
8. Card reader or computer with built in card reader.
9. A case for the Pi (optional)

Download the latest version of Raspbian (Stretch as of this writing) operating system from here. Insert the SD card in the adapter that ships with it and put the adapter with the SD card into your card reader. Copy the Raspian operating system image onto the SD card by using these instructions:

• WIndows instructions
• Mac OSX instructions
• Linux instructions

This will take some time to copy the image to your SD card. Assemble the rest of the RPi while you are waiting.

Insert the wifi adapter in one of the USB ports. Insert the keyboard and mouse dongle into one of the other USB ports. Connect a monitor to the Raspberry Pi with the HDMI cable.

When the Raspbian image has completed installing on the SD card, remove the SD card from the adapter and insert it into the SD card slot on the underside of the Raspberry Pi. Then insert the power adapter into the micro USB port and power up the Raspberry Pi.

Once the Raspberry Pi has finished booting up set up your wifi connection on the Raspberry PI by opening a terminal window and edit the wpa_supplicant.conf file by using the following command:

sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

Change the country to your two letter country code.

Add your Wifi access point SSID and password at the bottom of the file:

network={
ssid="Your Wifi SSID"
psk="yourWifiPassword"
}

One thing to note: The default keyboard setting is to use a GB configuration. For those of us in the US it places some of the special characters in different places, mainly the @ and the " symbols are switched.

Save the file and exit nano.

Bring the WIfi connection up by typing:

ifup

or by rebooting the Raspberry PI with:

sudo reboot

When your Raspberry Pi has successfully connected to your Wifi you should see the Wifi symbol in the menu bar in the upper right corner of the screen for the Raspberry Pi.

You can now configure other options for your Pi. From a termnial window type:

sudo raspi-config

This will bring up the raspi-config interface an allow you to configure other options your Raspberry PI. You don't have to do this but there are a couple of things that you should do:

1. Change the default password. Don't leave devices on your network vulnerable by leaving the default passwords on your RPi for the pi and root users.
2. Set your location setting. This will give you the right keyboard settings, time settings and location for installing other software from the nearest repos. If you get the annoying PERL warnings about the locale cannot be set you can resolve it by using these instructions.
3. Expand the file system to use the entire SD card. This will give you access to the entire storage space on the HD card.

Feel free to look at the other options that are available to you through this interface. You can do other things like overclocking your CPU, set up ssh and ftp connections, and change your boot settings to boot to a command line or the desktop.

To do this we're going to use dnsmasq to set up the RPi to be a DHCP server and set up some custom DNS settings. This will allow the device connected to the RPi through ethernet to get an IP address from the RPi and also to for the RPi to pass DNS queries.

We'll also configure some iptables settings to make a NAT between the ethernet adapter and the Wifi connection.

First, install dnsmasq:

sudo apt-get install dnsmasq

Set your ethernet adapter to a static IP address

This will serve as a gateway for the device that you want to connect to the RPi ethernet port. Most Wifi routers use what's called a Private Network and set the IP range to something similar to:

192.168.1.1

For the ethernet adapter on your RPI you'll want to set that to an address that won't interfere with the routers ability to assign addresses, so we'll increment the subnet of the PRi to be:

192.168.2.1

Along with that you'll need to set up the the netmask to:

255.255.255.0

As well as the DCHP settings to broadcast what IP address are available:

network 192.168.2.0
broadcast 192.168.2.255

Use iptables to configure a NAT setting to share the Wifi connection with the ethernet port
NAT stands for Network Address Translation. This allows a single IP address to server as a router on a network. So in this case the ethernet adapter on the RPi will serve as the router for whatever device you attach to it. The NAT settings will route the ethernet requests through the Wifi connection.

There are several commands to run here:

sudo iptables -F
sudo iptables -t nat -F
sudo iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
sudo iptables -A FORWARD -i wlan0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i eth0 -o wlan0 -j ACCEPT

Configure the dnsmasq settings

The first thing to do is to turn on IP forwarding. This is done by putting a single number 1 in the /proc/sys/net/ipv4/ip_forward file:

sudo nano /proc/sys/net/ipv4/ip_forward

Put a 1 on the first line and then exit and save. Hint: you also may have to edit /etc/sysctl.conf and uncomment this line:

net.ipv4.ip_forward=1

Next set up ip routing:

sudo ip route del 0/0 dev eth0 &> /dev/null
a=`route | awk "/${wlan}/"'{print $5+1;exit}'`
sudo route add -net default gw 192.168.2.1 netmask 0.0.0.0 dev eth0 metric $a

The last thing to do is edit your /etc/dnsmasq.conf file and include these settings;

interface=eth0
bind-interfaces
server=8.8.8.8
domain-needed
bogus-priv
dhcp-range=192.168.2.2,192.168.2.100,12h

Then run this command to start your dnsmasq services:

sudo systemctl start dnsmasq

Now plug a CAT5 network cable into the device you want to include on the network and put the other end of the cable into the ethernet port on the RPi and you should be good to go! When we set up the ethernet interface we made it hot pluggable, so you should see the ethernet interface come up when you plug the device into the RPi.

This was a lot of work to get the network bridge up and running. You'll probably want this to run automatically every time your RPi boots up, so to do that we're going to need a script to run all of these commands for us. Luckily Arpit Agarwal has already created a script and is available for download here.

Don't worry about typing all those commands above and run this command from your home directory to download the script file:

https://raw.githubusercontent.com/arpitjindal97/raspbian-recipes/master/wifi-to-eth-route.sh

To get this file to run every time you boot your RPi you'll need to add a directive to your session autostart file:

nano /home/pi/.config/lxsession/LXDE-pi/autostart

and add this to the bottom of the file:

sudo bash /home/pi/wifi-to-eth-route.sh

Then just reboot the RPi and the script does all the work for you. You can also run this set up any time you want by running this command from a terminal:

sudo bash /home/pi/wifi-to-eth-route.sh