Creating an ad hoc Wi-Fi network¶

The purpose of this tutorial is to create a direct access to the Raspberry Pi 2 using a wireless connection, without the need of using a router or access point.

This tutorial has been tested on Raspbian wheezy distribution.

First of all we need to edit the network interfaces configuration, and what we are going to do is to assign a static address to our wifi interface and tell to the networking service to invoke the wpa_supplicant with custom parameters when the wifi go up and to kill the wpa_supplicant when the wifi go down.

Your configuration might be something like this if you are using Raspbian Jessie:

...
source-directory /etc/network/interfaces.d

auto lo
iface lo inet loopback

iface eth0 inet manual

allow-hotplug wlan0
iface wlan0 inet manual
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

allow-hotplug wlan1
iface wlan1 inet manual
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

Let’s open the configuration and start editing.

$ sudo nano /etc/network/interfaces

Replace the configuration of wlan0 or whatever interface you want to use with the configuration below:

allow-hotplug wlan0
iface wlan0 inet static
pre-up wpa_supplicant -Dwext -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf -B
post-down killall -q wpa_supplicant
#wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
address 192.168.10.1
netmask 255.255.255.0

iface wlan0 inet static

Define a static ip address, and doing this we don’t bother dhcp services.

pre-up wpa_supplicant -Dwext -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf -B

The networking service call wpa_supplicant with -D nl80211,wext, telling to the service to use the first driver that works for him. Unfortunately it picks nl80211 that doesn’t work in Ad-Hoc mode, at least on my system. So we leave only wext as available driver and it should works.

post-down killall -q wpa_supplicant

We kill wpa_supplicant when the interface go down. The networking service doesn’t kill it if we don’t use wpa-conf property so we have to do it.

address 192.168.10.1

The ip address we want to set for this machine.

netmask 255.255.255.0

The netmask we want to set for the network.

$ ps -ef | grep -v grep | grep dhcpcd

interface wlan0
static domain_name_servers=8.8.8.8
static domain_search=8.8.4.4

interface wlan0
static domain_name_servers=8.8.8.8
static domain_search=8.8.4.4

# set your address and gateway here
static ip_address=192.168.10.1
static routers=192.168.10.1

Now the other step to do is editing the Wi-Fi configuration file wpa_supplicant and add your ad hoc network.

Open the file with:

$ sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

Comment your previously access point if you have one, we need to disable it and add the new network as below:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

ap_scan=2
network={
        ssid="RaspiHoc"
        mode=1
        frequency=2432
        proto=WPA
        key_mgmt=WPA-NONE
        pairwise=NONE
        group=CCMP
        psk="myraspihoc"
        #id_str="raspihoc"
}

You might want to change ssid, psk and id_str before saving.

Bring the wifi down and reload the networking configuration:

$ sudo ifdown --force wlan0
$ sudo service networking reload

Bring the wifi up again and check if the new ad hoc network has been set with:

$ sudo ifup wlan0
$ iwconfig

wlan0   IEEE 802.11bg  ESSID:"RaspiHoc"  Nickname:"<WIFI@REALTEK>"
                Mode:Ad-Hoc  Frequency:2.412 GHz  Cell: 02:11:87:88:50:13
                ...

Check if Mode is set as Ad-Hoc and ESSID has the ssid you set. Then you might want to connect to the new network with your device.

After your device has been connected to the network you can check the next step with:

$ ip addr

...
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
link/ether 64:e5:99:fb:ff:66 brd ff:ff:ff:ff:ff:ff
inet 192.168.10.1/24 brd 192.168.10.255 scope global wlan0
        valid_lft forever preferred_lft forever

With ip addr you shoud be able to see if the network has been set with the right address, looking at my output inet 192.168.10.1/24, you can see my network has the address I set before.

Now you can connect directly to your Raspberry Pi 2 using his local address 192.168.10.1.

You will see that you can not use this network to access Internet. In case you want to be able to use internet using this network you have to install a new service bridge-utils, that will bridge the Internet connection on eth0 to wlan0:

$ sudo apt-get install bridge-utils

Then you need to add some lines on the network configuration file /etc/network/interfaces as below:

auto br0
iface br0 inet dhcp
bridge_ports eth0 wlan0

Bring down the wifi interface and reload the network configuration:

$ sudo ifdown --force wlan0
$ sudo service networking reload
$ sudo ifup wlan0

And you should be able to connect directly to your Raspberry Pi and using Internet connection all together.