Wireless

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Wireless Station

The default configuration for the wireless station interface is defined in /etc/network/interfaces.d/wlan0. The configuration specifies interface bring-up behavior, including starting the DHCP client for the device and setting the network configuration file for the WPA supplicant: 

auto wlan0

iface wlan0 inet manual
        pre-up ifconfig $IFACE up
        post-up dhclient -nw $IFACE
        wpa-conf /etc/wpa_supplicant.conf
        wpa-driver nl80211
        wpa-options -B


Bringing up Wireless Interface

The wireless interface (most commonly wlan0) can be brought up manually with: 

ifconfig <interface> up

To check the naming of the interfaces available, including those that have yet to be brought up, the -a flag can be used. 

$ ifconfig -a

lo        Link eoopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

sit0      Link encap:IPv6-in-IPv4  
          NOARP  MTU:1480  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropps:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

wlan0     Link encap:Ethernet  HWaddr e0:e5:cf:00:ff:22  
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

Wireless Naming Rules

The wireless naming will automatically be enumerated by udev based on hardware address within /etc/udev/rules.d/70-persistent-net.rules. udev will create a new and unique name for the interface if it is not listed within this rules file. This will ensure that the interface name will always be the same when the system boots up. Removing the list of interfaces from within this file will cause udev to regenerate interface names on the next reboot. In the following example, a name of "wlan0" has been given to the wireless interface: 

# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# Unknown net device (/devices/amba.2/e000b000.ps7-ethernet/net/eth0) (xemacps)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0a:35:00:01:22", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"


# Unknown net device (/devices/soc0/amba/e0101000.sdhci/mmc_host001/mmc1:0001:2/wl18xx.0.auto/net/wlan0) (wl18xx_driver)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="e0:e5:cf:00:ff:22", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="wlan*", NAME="wlan0"

Wireless Configuration on Boot

The wireless interface bring-up behaviour can be configured within /etc/network/interfaces.d.

Connecting to Networks (wpa_supplicant)

A network connection can be established by starting the wpa_supplicant daemon. The WPA supplicant requires a configuration file with a list of network configurations to use for connection. 

$ wpa_supplicant -B -Dnl80211 -iwlan1 -c/etc/wpa_supplicant.conf
Successfully initialized wpa_supplicant

Checking Network Connection

iw dev <interface> link

If connected to a network the output will show the details of the connection: 

$ iw dev wlan0 link

Connected to 12:34:56:78:9a:bc (on wlan0)
	SSID: MyNetwork
        freq: 2437
        RX: 32843 bytes (117 packets)
        TX: 1303 bytes (12 packets)
        signal: -44 dBm
        tx bitrate: 150.0 MBit/s MCS 7 40MHz short GI

        bss flags:      short-preamble short-slot-time
        dtim period:    1
        beacon int:     100



$ iw dev wlan0 link

Not connected.

Getting an IP Address (dhclient)

dhclient <interface>


Checking IP Address and Connectivity

Checking Interface Configuration/Connection (ifconfig)

$ ifconfig

wlan0     Link encap:Ethernet  HWaddr e0:e5:cf:00:ff:22  
          inet addr:10.0.111.160  Bcast:10.0.111.255  Mask:255.255.255.0
          inet6 addr: fe80::e2e5:cfff:fe00:ff22/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:201 errors:0 dropped:0 overruns:0 frame:0
          TX packets:11 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:54949 (54.9 KB)  TX bytes:1526 (1.5 KB)

Checking Internet Connection (ping)

$ ping google.com

PING google.com (216.58.194.206) 56(84) bytes of data.
64 bytes from sfo03s01-in-f14.1e100.net (216.58.194.206): icmp_seq=1 ttl=54 time=18.0 ms


Network Interface Configuration

Files defining the network configuration information can be created within the /etc/network/interfaces.d directory which is sourced when ifup -a is run (typically from within the network boot script sourced from /etc/init.d/networking). The following example brings up the interface on boot up by identifying the inteface with auto wlan0. The rules defined after iface wlan0 inet manual specify the the set of commands to execute as the interface is controlled by the system. The commands described earlier have been combined to automatically bring up the interface and use the WPA supplicant to connect to available networks listed in the configuration file /etc/wpa_supplicant.conf. 

#### wlan0 configuration ####
auto wlan0
iface wlan0 inet manual
    pre-up ifconfig $IFACE up
    up wpa_supplicant -B -Dnl80211 -i$IFACE -c/etc/wpa_supplicant.conf
    up dhclient $IFACE
    down ifconfig $IFACE down

The combination of files within /etc/network/interfaces.d and the /etc/udev/rules.d/70-persistent-net.rules create the rules for naming and controlling the bring-up/down of the network interfaces.

Wireless Access Point

Network Interface Configuration

auto wlan1

iface wlan1 inet static
        address 10.0.110.2
        netmask 255.255.255.0
        hostapd /etc/hostapd.conf

Hostapd

ifupdown Script

A script responsible for bringing up the hostapd resides in the /etc/network/if-up.d directory for execution after the network interface has been brought up. The hostapd stanza of the network interface configuration is what acts as the switch for the hostapd script. The script is responsible for, in addition to bringing up the access point, setting the default SSID in hostapd.conf. If the SSID has not already been set when the hostapd script is executed, a default SSID will be generated using the last 6 octets of the interface MAC address. If the SSID has already been set, either by a previous execution of the script, or by the user, the script does not modify the SSID. 

if-up.d/hostapd --> /etc/hostapd/ifupdown.sh

hostapd.conf

interface=wlan1
#bridge=br0
driver=nl80211
logger_syslog=-1
logger_syslog_level=2
logger_stdout=-1
logger_stdout_level=2
ctrl_interface=/var/run/hostapd
#ctrl_interface_group=wheel
#ssid=
country_code=US
ieee80211d=1
ieee80211h=1
hw_mode=g
channel=11
# acs_whitelist=1 2 3 4 5 6 7 8 9 10 11
ap_channel_sync=1
beacon_int=100
dtim_period=2
max_num_sta=10
supported_rates=10 20 55 110 60 90 120 180 240 360 480 540
basic_rates=10 20 55 110 60 120 240
preamble=1
macaddr_acl=0
#deny_mac_file=/etc/hostapd.deny
auth_algs=3
ignore_broadcast_ssid=0
#vendor_elements=dd0411223301
tx_queue_data3_aifs=7
tx_queue_data3_cwmin=15
tx_queue_data3_cwmax=1023
tx_queue_data3_burst=0
tx_queue_data2_aifs=3
tx_queue_data2_cwmin=15
tx_queue_data2_cwmax=63
tx_queue_data2_burst=0
tx_queue_data1_aifs=1
tx_queue_data1_cwmin=7
tx_queue_data1_cwmax=15
tx_queue_data1_burst=3.0
tx_queue_data0_aifs=1
tx_queue_data0_cwmin=3
tx_queue_data0_cwmax=7
tx_queue_data0_burst=1.5
wme_enabled=1
uapsd_advertisement_enabled=1
wme_ac_bk_cwmin=4
wme_ac_bk_cwmax=10
wme_ac_bk_aifs=7
wme_ac_bk_txop_limit=0
wme_ac_bk_acm=0
wme_ac_be_aifs=3
wme_ac_be_cwmin=4
wme_ac_be_cwmax=10
wme_ac_be_txop_limit=0
wme_ac_be_acm=0
wme_ac_vi_aifs=2
wme_ac_vi_cwmin=3
wme_ac_vi_cwmax=4
wme_ac_vi_txop_limit=94
wme_ac_vi_acm=0
wme_ac_vo_aifs=2
wme_ac_vo_cwmin=2
wme_ac_vo_cwmax=3
wme_ac_vo_txop_limit=47
wme_ac_vo_acm=0
ap_max_inactivity=10000
disassoc_low_ack=1
ieee80211n=1
ht_capab=[SHORT-GI-20][GF]
wep_rekey_period=0
eap_server=1
own_ip_addr=127.0.0.1
wpa=2
wpa_passphrase=snickerdoodle
wpa_group_rekey=0
wpa_gmk_rekey=0
wpa_ptk_rekey=0
ap_table_max_size=255
ap_table_expiration_time=60
wps_state=2
ap_setup_locked=1
uuid=12345678-9abc-def0-1234-56789abcdef0
device_name=Sitara
manufacturer=TexasInstruments
model_name=TI_Connectivity_module
model_number=wl18xx
serial_number=12345
device_type=0-00000000-0
config_methods=virtual_display virtual_push_button keypad


DHCP Server

/etc/default/isc-dhcp-server 

INTERFACES="wlan1"


Server Configuration

#
# Configuration file for ISC dhcpd for Debian
#

ddns-update-style none;
log-facility local7;


subnet 10.0.110.0 netmask 255.255.255.0 {

        range                           10.0.110.10     10.0.110.100;
        option routers                  10.0.110.2;
        option broadcast-address        10.0.110.255;
        option domain-name              "local";
        default-lease-time              600;
        max-lease-time                  7200;
}
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