Share Raspberry Pi 4 Internet from Wifi to Ethernet

This tutorial starts from a fresh installed OS Lite and static ip address on eth0 and wlan0. We should connect on wireless instead of ethernet. In this tutorial, I’m configuring according to my network address but yours maybe different. You may follow this step by step tutorial but on ip addresses, please change according to your home network settings.

You may check my tutorial about how to install Raspberry PI OS Lite and setup static Ip address.

Let’s begin by connecting on Raspberry Pi wifi and update the system.

sudo apt-get update

My static ip addresses:

ifconfig

# eth0  (cable) : 192.168.1.10
# wlan0 (wifi)  : 192.168.1.11

I’m having static ip address using DHCPCD method. Here’s my configuration

sudo nano /etc/dhcpcd.conf

To check where the wifi ssid and password is saved:

sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

SET STATIC IP ADDRESS

Now that we are sure we are connected on wifi and with static ip configured, we can now start to change from DHCP to NETWORKING static ip address method.

sudo nano /etc/network/interfaces

Paste this:

auto eth0
iface eth0 inet static
    address 192.168.5.1
    netmask 255.255.255.0
    network 192.168.5.0
    broadcast 192.168.5.255

allow-hotplug wlan0
iface wlan0 inet static
    address 192.168.1.11
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 192.168.1.1
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

Enable networking service

sudo systemctl enable networking
sudo systemctl disable dhcpcd

Deny interfaces on dhcpcd

denyinterfaces eth0
denyinterfaces wlan0

Restart

sudo reboot

INSTALL DHCP SERVER

We’ll choose Dnsmasq application

sudo apt install dnsmasq

To configure, stop the service first

systemctl stop dnsmasq

Backup the default configuration:

sudo mv /etc/dnsmasq.conf /etc/dnsmasq.conf.orig

sudo nano /etc/dnsmasq.conf

Paste this:

interface=eth0
listen-address=192.168.5.1
dhcp-range=192.168.5.50,192.168.5.100,12h
server=8.8.8.8
bind-interfaces
domain-needed
bogus-priv

Start the service

systemctl start dnsmasq

SHARING INTERNET FROM WIFI AND SHARE TO LAN

To share Raspberry Pi internet from wifi, we have to configure ipv4 forward and set iptables routing connection from wlan0 to eth0.

sudo nano /etc/sysctl.conf

uncommend this line by removing # character:

net.ipv4.ip_forward=1

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

Change iptables

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

Save the changes

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

Open RC

sudo nano /etc/rc.local

Paste this on top of exit 0

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

Save, exit and reboot

sudo reboot

To test if it works, turn off your computer’s wifi. Plug the ethernet cable on your computer and the other end to your raspberry pi. You computer should get IP address distributed in your ethernet interface. To check on windows 10, run command and type ipconfig. On my computer I’m getting IP address starting from 192.168.5…

Open your internet browser and check some websites. If you got this right, you should have internet.

UNINSTALL ALL THE CHANGES WE MADE

In case you don’t need this anymore and want to delete all changes we made, please follow these steps. Please remember this is not a continuation of the tutorial.

Connect to wifi and login

Uninstalling Dnsmasq:

systemctl stop dnsmasq
sudo mv /etc/dnsmasq.conf.orig /etc/dnsmasq.conf
sudo apt remove dnsmasq

Restore original network settings

sudo nano /etc/sysctl.conf

#Add # at the beginning:
  #net.ipv4.ip_forward=1


sudo nano /etc/rc.local
remove this line: 
  iptables-restore < /etc/iptables.ipv4.nat

Write script to restore default iptable

nano reset_firewall.sh

Paste this code:

#!/bin/sh
echo "Resetting the IP Tables"
ipt="/sbin/iptables"
## Failsafe - die if /sbin/iptables not found
[ ! -x "$ipt" ] && { echo "$0: \"${ipt}\" 
command not found."; exit 1; }
$ipt -P INPUT ACCEPT
$ipt -P FORWARD ACCEPT
$ipt -P OUTPUT ACCEPT
$ipt -F
$ipt -X
$ipt -t nat -F
$ipt -t nat -X
$ipt -t mangle -F
$ipt -t mangle -X
$ipt -t raw -F
$ipt -t raw -X

Save, exit and run:

sudo sh reset_firewall.sh

Restore network interface

sudo nano /etc/network/interfaces

Delete your static ip address entry

Now open DHCPCD config file

sudo nano /etc/dhcpcd.conf

Remove this entry

denyinterfaces eth0
denyinterfaces wlan0

Switch back to DHCPCP service

sudo systemctl disable networking
sudo systemctl enable dhcpcd

sudo reboot

That’s it. You are done.