How to use your Raspberry Pi 3 as a wireless access point

 

The Raspberry Pi can do a lot, especially now that the new Raspberry Pi comes with wireless capabilities already on board. It can take the place of a ton of different (and more expensive) devices – including a router! If you turn your Raspberry Pi into a wireless access point, you can make it act as a router. It’s not the most powerful thing in the world, but it does work, and the project is a lot of fun.

How to use your Raspberry Pi as a wireless access point

We’re going to get into the command line a bit here, but this project isn’t really all that difficult. All we’re really doing is using Raspbian and installing a couple packages that give the Pi the ability to do router-like things like assign IP addresses to devices that connect to it.

Step 1: Install and update Raspbian

Check out our complete guide to installing Raspbian for the details on this one. Then plug everything in and hop into the terminal and check for updates and ugrades:

sudo apt-get update

Step 2: Install hostapd and dnsmasq

These are the two programs we’re going to use to make your Raspberry Pi into a wireless access point. To get them, just type these lines into the terminal:

sudo apt-get install hostapd

sudo apt-get install dnsmasq

Both times, you’ll have to hit y to continue. hostapd is the package that lets us create a wireless hotspot using a Raspberry Pi, and dnsmasq is an easy-to-use DHCP and DNS server.

We’re going to edit the programs’ configuration files in a moment, so let’s turn the programs off
before we start tinkering:

sudo systemctl stop hostapd

sudo systemctl stop dnsmasq

Step 3: Configure a static IP for the wlan0 interface

For our purposes here, I’m assuming that we’re using the standard home network IP addresses, like 192.168.###.###. Given that assumption, let’s assign the IP address 192.168.22.10 to the wlan0
interface by editing the dhcpcd configuration file. Start editing with this command:

sudo nano /etc/dhcpcd.conf

Now that you’re in the file, add the following lines at the end:

interface wlan0

static ip_address=192.168.22.10/24

denyinterfaces eth0

denyinterfaces wlan0

(The last two lines are needed in order to make our bridge work –- but more on that in
Step 8.)

After that, press Ctrl+X, then Y, then Enter to save the file and exit the editor.

Step 4: Configure the DHCP server (dnsmasq)

We’re going to use dnsmasq as our DHCP server. The idea of a DHCP server is to
dynamically distribute network configuration parameters, such as IP addresses, for
interfaces and services.

dnsmasq’s default configuration file contains a lot of unnecessary information, so
it’s easier for us to start from scratch. Let’s rename the default configuration file and
write a new one:

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

sudo nano /etc/dnsmasq.conf

You’ll be editing a new file now, and with the old one renamed, this is the config file that dnsmasq will use. Type these lines into your new configuration file:

interface=wlan0

  dhcp-range=192.168.22.11,192.168.22.30,255.255.255.0,24h

The lines we added mean that we’re going to provide IP addresses between 192.168.22.11 and 192.168.22.30 for the wlan0 interface.

Step 5: Configure the access point host software (hostapd)

Another config file! This time, we’re messing with the hostapd config file. Open ‘er up:

sudo nano /etc/hostapd/hostapd.conf

This should create a brand new file. Type in this:

interface=wlan0

bridge=br0

hw_mode=g

channel=6

wmm_enabled=0

macaddr_acl=0

auth_algs=1

ignore_broadcast_ssid=0

wpa=2

wpa_key_mgmt=WPA-PSK

wpa_pairwise=TKIP

rsn_pairwise=CCMP

ssid=NETWORK

wpa_passphrase=PASSWORD

Note that where I have “NETWORK” and “PASSWORD,” you should come up with your own names. This is how you’ll join the Pi’s network from other devices.

We still have to show the system the location of the configuration file:

sudo nano /etc/default/hostapd

In this file, track down the line that says #DAEMON_CONF=”” – delete that # and put the path to our config file in the quotes, so that it looks like this:

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

The # keeps the line from being read as code, so you’re basically bringing this line to life here while giving it the right path to our config file.

Step 6: Set up traffic forwarding

The idea here is that when you connect to your Pi, it will forward the traffic over your Ethernet cable. So we’re going to have wlan0 forward via Ethernet cable to your modem. This involves editing yet another config file:

sudo nano /etc/sysctl.conf

Now find this line:

#net.ipv4.ip_forward=1

…and delete the “#” – leaving the rest, so it just reads:

net.ipv4.ip_forward=1

Step 7: Add a new iptables rule

Next, we’re going to add IP masquerading for outbound traffic on eth0 using iptables:

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

…and save the new iptables rule:

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

To load the rule on boot, we need to edit the file /etc/rc.local and add the following
line just above the line exit 0:

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

Step 8: Enable internet connection

Now the Raspberry Pi is acting as an access point to which other devices can connect. However, those devices can’t use the Pi to access the internet just yet. To make the possible, we need to build a bridge that will pass all traffic between the wlan0 and eth0 interfaces.

To build the bridge, let’s install one more package:

sudo apt-get install bridge-utils

We’re ready to add a new bridge (called br0):

sudo brctl addbr br0

Next, we’ll connect the eth0 interface to our bridge:

sudo brctl addif br0 eth0

Finally, let’s edit the interfaces file:

sudo nano /etc/network/interfaces

…and add the following lines at the end of the file:

auto br0

iface br0 inet manual

bridge_ports eth0 wlan0

Step 9: Reboot

Now that we’re ready, let’s reboot with sudo reboot.

Now your Pi should be working as a wireless access point. Try it out by hopping on another device and looking for the network name you used back in step 5.

Problem with hostapd on Rasbian Stretch

sudo systemctl start hostapd

Failed to start hostapd.service: Unit hostapd.service is masked.

Solution

The latest update to Raspbian (2019-03-09) has changed hostapd "wpa (2:2.6-10)".

To ensure hostapd runs on boot run the following commands:

sudo systemctl unmask hostapd

sudo systemctl enable hostapd

 

Source

https://thepi.io/how-to-use-your-raspberry-pi-as-a-wireless-access-point/