Chapter 13: A Wireless Access Point

The Raspberry Pi can be used as a wireless access point, running a standalone network. This can be done using the inbuilt wireless features of the Raspberry Pi 3 or Raspberry Pi Zero W, or by using a suitable USB wireless dongle that supports access points.

Note that this documentation was tested on a Raspberry Pi 3, and it is possible that some USB dongles may need slight changes to their settings. If you are having trouble with a USB wireless dongle, please check the forums.

To add a Raspberry Pibased access point to an existing network, see this section.

In order to work as an access point, the Raspberry Pi will need to have access point software installed, along with DHCP server software to provide connecting devices with a network address. Ensure that your Raspberry Pi is using an uptodate version of Raspbian (dated 2017 or later).

Use the following to update your Raspbian installation:

sudo aptget update

sudo aptget distupgrade

Install all the required software in one go with this command:

sudo aptget install dnsmasq hostapd

Since the configuration files are not ready yet, turn the new software off as follows:

sudo systemctl stop dnsmasq

sudo systemctl stop hostapd

Configuring A Static Ip

We are configuring a standalone network to act as a server, so the Raspberry Pi needs to have a static IP address assigned to the wireless port. This documentation assumes that we are using the standard 192.168.x.x IP addresses for our wireless network, so we will assign the server the IP address 192.168.0.1. It is also assumed that the wireless device being used is wlan0.

First, the standard interface handling for wlan0 needs to be disabled. Normally the dhcpcd daemon (DHCP client) will search the network for a DHCP server to assign a IP address to wlan0. This is disabled by editing the configuration file:

sudo nano /etc/dhcpcd.conf

Add denyinterfaces wlan0 to the end of the file (but above any other added interface lines) and save the file.

To configure the static IP address, edit the interfaces configuration file with:

sudo nano /etc/network/interfaces

Find the wlan0 section and edit it so that it looks like the following:

allowhotplug wlan0

iface wlan0 inet static

address 192.168.0.1

netmask 255.255.255.0

network 192.168.0.0

Now restart the dhcpcd daemon and set up the new wlan0 configuration:

sudo service dhcpcd restart

sudo ifdown wlan0

sudo ifup wlan0

Configuring The Dhcp Server (Dnsmasq)

The DHCP service is provided by dnsmasq. By default, the configuration file contains a lot of information that is not needed, and it is easier to start from scratch. Rename this configuration file, and edit a new one:

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

sudo nano /etc/dnsmasq.conf

Type or copy the following information into the dnsmasq configuration file and save it:

interface=wlan0 # Use the require wireless interface usually wlan0

dhcprange=192.168.0.2,192.168.0.20,255.255.255.0,24h

So for wlan0, we are going to provide IP addresses between 192.168.0.2 and 192.168.0.20, with a lease time of 24 hours. If you are providing DHCP services for other network devices (e.g. eth0), you could add more sections with the appropriate interface header, with the range of addresses you intend to provide to that interface.

There are many more options for dnsmasq; see the dnsmasq documentation for more details.

Configuring The Access Point Host Software (Hostapd)

You need to edit the hostapd configuration file, located at /etc/hostapd/hostapd.conf, to add the various parameters for your wireless network. After initial install, this will be a new/empty file.

sudo nano /etc/hostapd/hostapd.conf

Add the information below to the configuration file. This configuration assumes we are using channel 7, with a network name of NameOfNetwork, and a password AardvarkBadgerHedgehog. Note that the name and password should not have quotes around them.

interface=wlan0

driver=nl80211

ssid=NameOfNetwork

hw_mode=g

channel=7

wmm_enabled=0

macaddr_acl=0

auth_algs=1

ignore_broadcast_ssid=0

wpa=2

wpa_passphrase=AardvarkBadgerHedgehog

wpa_key_mgmt=WPAPSK

wpa_pairwise=TKIP

rsn_pairwise=CCMP

We now need to tell the system where to find this configuration file.

sudo nano /etc/default/hostapd

Find the line with #DAEMON_CONF, and replace it with this:

DAEMON_CONF=”/etc/hostapd/hostapd.conf”

Start It Up

Now start up the remaining services:

sudo service hostapd start

sudo service dnsmasq start

Using a wireless device, search for networks. The network SSID you specified in the hostapd configuration should now be present, and it should be accessible with the specified password.

If SSH is enabled on the Raspberry Pi access point, it should be possible to connect to it from another Linux box (or a system with SSH connectivity present) as follows, assuming the pi account is present:

ssh [email protected]

By this point, the Raspberry Pi is acting as an access point, and other devices can associate with it. Associated devices can access the Raspberry Pi access point via its IP address for operations such as rsync, scp, or ssh.

Using The Raspberry Pi3 As An Access Point To Share An Internet Connection

One common use of the Raspberry Pi as an access point is to provide wireless connections to a wired Ethernet connection, so that anyone logged into the access point can access the internet, providing of course that the wired Ethernet on the Pi can connect to the internet via some sort of router.

To do this, a ‘bridge’ needs to put in place between the wireless device and the Ethernet device on the access point Raspberry Pi. This bridge will pass all traffic between the two interfaces. Install the following packages to enable the access point setup and bridging.

sudo aptget install hostapd bridgeutils

Since the configuration files are not ready yet, turn the new software off as follows:

sudo systemctl stop hostapd

Bridging creates a higherlevel construct over the two ports being bridged. It is the bridge that is the network device, so we need to stop the eth0 and wlan0 ports being allocated IP addresses by the DHCP client on the Raspberry Pi.

sudo nano /etc/dhcpcd.conf

Add denyinterfaces wlan0 and denyinterfaces eth0 to the end of the file (but above any other added interface lines) and save the file.

Add a new bridge, which in this case is called br0.

sudo brctl addbr br0

Connect the network ports. In this case, connect eth0 to wlan0.

sudo brctl addif br0 eth0 wlan0

Now the interfaces file needs to be edited to adjust the various devices to work with bridging. sudo nano /etc/network/interfaces make the following edits.

Change the wlan entry to manual if it not already so, and remove any other entries e.g. any static address.

allowhotplug wlan0

iface wlan0 inet manual

Add the bridging information at the end of the file.

# Bridge setup

auto br0

iface br0 inet dhcp

bridge_ports eth0 wlan0

The access point setup is almost the same as that shown in the previous section. Follow the instructions above to set up the hostapd.conf file, but add bridge=br0 below the interface=wlan0 line, and remove or comment out the driver line.

interface=wlan0

bridge=br0

#driver=nl80211

...

Now reboot the Raspberry Pi3.

There should now be a functioning bridge between the wireless LAN and the Ethernet connection on the Raspberry Pi, and any device associated with the Raspberry Pi access point will act as if it is connected to the access point’s wired Ethernet.

The ifconfig command will show the bridge, which will have been allocated an IP address via the wired Ethernet’s DHCP server. The wlan0 and eth0 no longer have IP addresses, as they are now controlled by the bridge. It is possible to use a static IP address for the bridge if required, but generally, if the Raspberry Pi access point is connected to a ADSL router, the DHCP address will be fine.