In very simple terms, wifi connection is determined by the hardware (wifi dongle) the driver (which makes the hardware compatible) and the configuration files (which makes the software work) which also include the Wifi encryption settings, of which there are 4.

• WPA
• WPA2
• WEP
• Open Network

Each network has its own name called the SSID or ESSID and some of them can be hidden or invisible which leaves the last main option

• Hidden SSID

There are two main configuration files that can be edited: /etc/network/interfaces, and /etc/wpa_supplicant/wpa_supplicant.conf

Interfaces can be used on its own, but wpa_supplicant.conf is something that requires editing of interfaces and wpa_supplicant.conf.

For wpa_supplicant conf you can either have a static list of networks or use wpa-roam which enables you to connect to multiple networks on the fly but you have to change the config variable to this iface wlan0 inet manual instead of dhcp.

So without further ado, here is a complete list of configuration options for the 5 different types of wifi in interfaces and in wpa_supplicant.

/etc/network/interfaces

Interfaces

WPA/WPA2

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0
iface wlan0 inet dhcp
   wpa-ssid "Your Wireless Network Name"
   wpa-psk "Your Wireless Network Password"

WEP

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0
iface wlan0 inet dhcp
  wireless-essid NETWORK_NAME
  wireless-key NETWORK_PASSWORD

Open Network

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0
iface wlan0 inet dhcp
  wireless-essid UR_ESSID
  wireless-mode managed

Hidden SSID

wpa-ssid "UR_ESSID"
wpa-psk "Password"
wpa-scan-ssid 1

wpa_supplicant.conf

WPA2

Interfaces (roaming-- Preferable because it reconnects after network drop)

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
#The following line specified in /etc/network/interfaces will activate and configure each 'default' network in wpa_supplicant.conf with DHCP upon a successful connection to an access point (this line needs to be here for wpa-roam)
iface default inet dhcp

Interfaces (non-roaming)

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0
iface wlan0 inet dhcp
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
#The following line specified in /etc/network/interfaces will activate and configure each 'default' network in wpa_supplicant.conf with DHCP upon a successful connection to an access point
iface default inet dhcp

Interfaces (static IP)

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
#id_str is the name of the network you setup in wpa_supplicant.conf
iface id_str inet static
address 192.168.0.104
netmask 255.255.255.0
gateway 192.168.0.1
#The following line specified in /etc/network/interfaces will activate and configure each 'default' network in wpa_supplicant.conf with DHCP upon a successful connection to an access point

wpa_supplicant

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

network={
    ssid="Your SSID Here"
    proto=RSN
    key_mgmt=WPA-PSK
    pairwise=CCMP TKIP
    group=CCMP TKIP
    psk="YourPresharedKeyHere"
# add the following line with your chosen ID and reference it a described in interfaces
    id_str="home_server"
}

WPA/WPA2

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

network={
    ssid="Your SSID Here"
    psk="Password"
}

WEP

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

network={
     ssid="YOURWLANSSID"
     key_mgmt=NONE
     wep_tx_keyidx=0 #this forces it to use wep_key0
     wep_key0=YOURWEPKEY
}

Open Network

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

network={
    ssid="Your SSID Here"
    key_mgmt=NONE
}

Hidden

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

network={
    ssid="Your SSID Here"
    key_mgmt=NONE
    scan_ssid=1
}

iwlist perametres

Code:

sudo iwlist wlan0 scan | awk '/IE: WPA/ || /ESSID:/ || /IE: IEEE/ || /Encryption/'

Results

#WPA
Encryption key:on
ESSID:"Network SSID"
IE:WPA Version 1

#WPA/WPA2
Encryption key:on
ESSID:"Network SSID2"
IE:WPA Version 1
IE: IEEE 802.11i/WPA2 Version 1

#WEP
Encryption key:on
ESSID:"Network SSID3"

#Open Network
Encryption key:off
ESSID:"Network SSID4"