Use a Raspberry Pi 3 as an access point

Raspberry Pis are awesome [citation needed].

This post is about how to setup a WiFi with a Raspberry Pi 3. It describes what packages you have to install and one example is shown how to configure them. In the end you will have an Raspberry Pi 3, which is connected through ethernet to the internet. The Pi provides an SSID and takes care that the traffic between WiFi and Ethernet is forwarded.

This tutorial basically follows the instructions on http://elinux.org/RPI-Wireless-Hotspot, except that it uses dnsmasq instead of udhcpd.

Steps

Operating system

Download and install an operating system for the Raspberry Pi. I used “Raspbian” and followed this description:

https://www.raspberrypi.org/documentation/installation/installing-images/mac.md

Before you unmount the flashed card, create a file named ssh in the boot segment on the disk. Otherwise you won’t be able to SSH into the Raspberry Pi.

Installations

Connect the Pi to your local network (through ethernet), search for the little rascal (i.e. using nmap) and connect to it via ssh.

When logged in, you will have to install at least 2 packages: dnsmasq and hostapd. I always love to have vim, so here’s what I did:

sudo apt-get update
sudo apt-get install vim
sudo apt-get install dnsmasq
sudo apt-get install hostapd

Configure the wlan interface

Now, let’s edit the iface wlan0 part in /etc/network/interfaces, make sure it is static and has following properties:

allow-hotplug wlan0
iface wlan0 inet static
address 10.0.0.1
netmask 255.255.255.0
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

Behold, that I used the address 10.0.0.1 as static IP. We will have to use the same IP for the DHCP configuration.

At this point you should quickly restart the networking service.

sudo service networking restart

ifconfig wlan0 should then show the applied changes on in the wlan0 interface.

Configure DNSmasq

The Pi will have to manage the clients IP address (DHCP) on the wlan0 interface. I used DNSmasq for the DHCP server, but it should work fine with any other DHCP servers.

However, let’s edit /etc/dnsmasq.con

domain-needed
bogus-priv
interface=wlan0
listen-address=10.0.0.1
dhcp-range=10.0.0.2,10.0.0.254,12h
dhcp-option=option:router,10.0.0.1
dhcp-authoritative

Note that the Pi’s static IP address is used for listen-address and dhcp-option=option:router. For more information about that, consider reading http://www.thekelleys.org.uk/dnsmasq/doc.html. ;-)

Portforwarding (route wlan0 to eth0)

The next step affects iptables. I am no expert in this, so I basically just copy pasted that stuff and ensured that the in -i and out -o parameters made sense.

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

In a nutshell, it allows that general traffic/communication is allowed between the interfaces wlan0 (wireless) and eth0 (ethernet). In order that the iptables rules apply immediately, you’ll have to do this:

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

In order that the iptables rules are considered after reboot, edit /etc/sysctl.conf, and uncomment this line:

net.ipv4.ip_forward=1

Finally persist the iptables rules, otherwise they get truncated after reboot. I used a package iptables-persistent which persists the rules right during installation which is pretty convenient.

sudo apt-get install iptables-persistent

Configure the access point

Now it get’s interesting. We can create our own SSID and define a password. Therefore create /etc/hostapd/hostapd.conf and paste and save this:

interface=wlan0 driver=nl80211
ssid=SIMPLIFICATOR-WIFI
hw_mode=g
channel=6
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=YOUR-INCREDIBLY-SECURE-PASSWORD
wpa_key_mgmt=WPA-PSK
#wpa_pairwise=TKIP  # You better do not use this weak encryption (only used by old client devices)
rsn_pairwise=CCMP
ieee80211n=1          # 802.11n support
wmm_enabled=1         # QoS support
ht_capab=[HT40][SHORT-GI-20][DSSS_CCK-40]

Let’s connect the above config to the default hostapd config, edit /etc/default/hostapd and make sure DAEMON_CONF is uncommented and points to the config file.

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

Services (hostapd & dnsmasq)

Lastly, let’s restart the services and enable them, so that the start automatically on boot.

sudo service hostapd restart
sudo service dnsmasq restart
sudo update-rc.d hostapd enable
sudo update-rc.d dnsmasq enable

That’s it

You should now see a WiFi named SIMPLIFICATOR-WIFI and connect to it using the passphrase YOUR-INCREDIBLY-SECURE-PASSWORD, or whatever values you have given it.

Insights

While writing the blog post I had several insights:

• Raspberry Pi 3 comes with an 2.4 GHz 802.11n (150 Mbit/s) WiFi. It’s always good to know the limits of the bandwidth.
• Even if you used a WiFi USB adapater with 1000 Mbit/s, the maximum speed would be 480 Mbit/s because of the USB 2 interface (!)
• I wasn’t able to configure the Pi, so that two WiFi dongles run simultaneously, so that you could extend the range of an existing WiFi without having the Pi connected to an ethernet cable.