Wi-Fi /etc/config/wireless

通过UCI配置wireless产生的配置文件位于 /etc/config/wireless.

如果设备有有线以太网端口, 无线wireless默认设置为 OFF 状态. 你可以在 /etc/config/wireless 中打开它，通过将 option disabled '1' 设置为 option disabled '0' (注释或删除掉该行也可以).

A typical wireless config file contains at least a pair of:

• wifi device (specifying general radio properties like channel, driver type and txpower)
• wifi interface (defining a wireless network on top of the wifi device).

The wifi-device refer to physical radio devices present on the system. The options present in this section describe properties common across all wireless interfaces on this radio device, such as channel or antenna selection.

A minimal wifi-device declaration may look like the example below. Note that identifiers and options may vary for different chipset types or drivers.

config	wifi-device	'wl0'
	option	type	'broadcom'
	option	channel	'6'

• wl0 is the internal identifier for the wireless adapter
• broadcom specifies the chipset/driver type
• 6 is the wireless channel the device operates on

The possible options for device sections are listed in the table below. Note that not all options are used for all chipset/driver types, refer to the comments for further details.

The options below are only used by the proprietary Broadcom driver (type broadcom).

The options below are only used by the Ubiquity Nanostation family of devices.

A complete wireless configuration contains at least one wifi-iface section per adapter to define a wireless network on top of the hardware. Some drivers support multiple wireless networks per device:

• broadcom if the core revision is greater or equal 9 (see dmesg | grep corerev)
• mac80211

A minimal example for a wifi-iface declaration is given below.

config	wifi-iface
	option	device		'wl0'
	option	network		'lan'
	option	mode		'ap'
	option	ssid		'MyWifiAP'
	option	encryption	'psk2'
	option	key		'secret passphrase'

• wl0 is the identifier for the underlying radio hardware
• lan specifies the network interface that the Wi-Fi is attached to.
• ap is the opetion mode, Access Point in this example
• MyWifiAP is the broadcasted SSID
• psk2 specifies the wireless encryption method, WPA2 PSK here
• secret passphrase is the secret WPA passphrase, at least 8 characters long

The common configuration option for wifi-iface sections are listed below.

Besides the WPA mode, the encryption option also specifies the group and peer ciphers to use. To override the cipher, the value of encryption must be given in the form mode+cipher. See the listing below for possible combinations. If the hwmode of the interface is set to ng or na, then the CCMP cipher is always added to the list.

To use the WPA3 modes as access point, it is required to install the hostapd-openssl package.

To use the WPA3 modes as station (client), it is required to install the wpa-supplicant-openssl package.

To support both access point and station modes with WPA3, it is possible to install the wpad-openssl package.

Listing of Access Point related options for WPA Enterprise.

Listing of Client related options for WPA Enterprise.

When using WPA Enterprise type PEAP with Active Directory Servers, the “auth” option must be set to “auth=MSCHAPV2” or “auth=PAP”.

option auth 'auth=MSCHAPV2'

or

option auth 'auth=PAP'

Complete description copied from upstream hostapd.conf example:

# Workaround for key reinstallation attacks
#
# This parameter can be used to disable retransmission of EAPOL-Key frames that
# are used to install keys (EAPOL-Key message 3/4 and group message 1/2). This
# is similar to setting wpa_group_update_count=1 and
# wpa_pairwise_update_count=1, but with no impact to message 1/4 and with
# extended timeout on the response to avoid causing issues with stations that
# may use aggressive power saving have very long time in replying to the
# EAPOL-Key messages.
#
# This option can be used to work around key reinstallation attacks on the
# station (supplicant) side in cases those station devices cannot be updated
# for some reason. By removing the retransmissions the attacker cannot cause
# key reinstallation with a delayed frame transmission. This is related to the
# station side vulnerabilities CVE-2017-13077, CVE-2017-13078, CVE-2017-13079,
# CVE-2017-13080, and CVE-2017-13081.
#
# This workaround might cause interoperability issues and reduced robustness of
# key negotiation especially in environments with heavy traffic load due to the
# number of attempts to perform the key exchange is reduced significantly. As
# such, this workaround is disabled by default (unless overridden in build
# configuration). To enable this, set the parameter to 1.
#wpa_disable_eapol_key_retries=1

Note that this workaround can't prevent attacks against Tunneled Direct-Link Setup (TDLS). You may also want to add the option tdls_prohibit=1 in order to make such an attack more complicated:

Listing of Wi-Fi Protected Setup related options.

Support for WPS is provided by packages wpad and hostapd-utils. Default package wpad-mini is not enough.

WPS is possible only when encryption PSK/PSK2 is selected.

Minimal steps needed to get WPS running:

• Add option wps_pushbutton '1 ' to a config wifi-iface section that is configured for WPA2-PSK in /etc/config/wireless
• opkg update
• opkg remove wpad-mini
• opkg install wpad hostapd-utils
• reboot

After rebooting, instead of pushing the WPS button, you can manually initiate the WPS process (which is safer than using the button if it doubles as a reset button):

hostapd_cli wps_pbc

When using WPS-PIN:

• Add option wps_label '1 ' to a config wifi-iface section that is configured for WPA2-PSK in /etc/config/wireless
• opkg update
• opkg remove wpad-mini
• opkg install wpad hostapd-utils
• reboot

After rebooting, the WPS PIN needs to be given to hostapd each time a station tries to connect. The PIN may NOT be used multiple times, as an active attacker can recover half of it during each try. The “any” keyword can be replaced by the specific stations EUUID, as printed in hostapd log.

hostapd_cli wps_pin any $PIN

Example:

# /etc/config/wireless
...
config wifi-iface
	option device 'radio0'
	option mode 'ap'
	option ssid 'My-WiFi-Home'
	option network 'lan'
	option encryption 'psk2'
	option key 'WiFipassword'
	option ieee80211w '0'
	option wps_pushbutton '1'

Wireless interfaces are brought up and down with the wifi command. To (re)start the wireless after a configuration change, use wifi, to disable the wireless, run wifi down. In case your platform carries multiple wireless devices it is possible to start or run down each of them individually by making the wifi command be followed by the device name as a second parameter. Note: The wifi command has an optional first parameter that defaults to up , i.e. start the device. To make the second parameter indeed a second parameter it is mandatory to give a first parameter which can be anything except down. E.g. to start the interface wlan2 issue: wifi up wlan2; to stop that interface: wifi down wlan2. If the platform has also e.g. wlan0 and wlan1 these will not be touched by stopping or starting wlan2 selectively.

To rebuild the configuration file, e.g. after installing a new wireless driver, remove the existing wireless configuration (if any) and use the wifi config command:

rm -f /etc/config/wireless
wifi config

The Wi-Fi channel width is the range of frequencies i.e. how broad the signal is for transferring data. Generally speaking, the bigger the channel width, the more data can be transmitted over the signal. But as with everything there are drawbacks. With larger channel widths, interference with others Wi-Fi networks or Bluetooth becomes a much larger issue, and making solid connections becomes much harder as well. Think of it like a highway. The wider the road, the more traffic (data) can pass through. On the other hand, the more cars (routers) you have on the road, the more congested the traffic becomes.

Wi-Fi standard allows 10, 20, 22, 40, 80 and 160 MHz but 10MHz is not used anymore, the 80 and 160 can be used only with 5 GHz frequency, and certain devices not being able to connect to APs with channel widths more than 40Mhz.

By default, the 2.4 GHz frequency uses a 20 MHz channel width. A 20MHz channel width is wide enough to span one channel. A 40 MHz channel width bonds two neighbouring 20 MHz channels together, forming a 40 MHz channel width; therefore, it allows for greater speed and faster transfer rates. One “control” channel functions as the main channel, and the other “extension” as the auxiliary channel. The main channel sends Beacon packets and data packets, and the auxiliary channel sends other packets. The extension channel can either be “above” or “below” the control channel, as long as it doesn't go outside the band. For example, if your control channel is 1, your extension channel has to “above”, because anything below channel 1 would be below the lowest frequency allowed in the 2.4GHz ISM band. The extension channel has to be contiguous with the edge of the control channel, without overlapping.

HT40+ means that centre frequency of the main 20 MHz channel is higher than that of the auxiliary channel, and HT40- otherwise. For example, if the centre frequency 149 and the centre frequency 153 reside on two 20 MHz channels, 149plus indicates that the two 20 MHz channels are bundled to form a 40 MHz channel.

When the HT40 mode is used in the 2.4 GHz frequency band, there is only one non-overlapping channel. Therefore, you are not advised to use the HT40 mode in the 2.4 GHz frequency band.

• HT20 High Throughput 20MHz, 802.11n
• HT40 High Throughput 40MHz, 802.11n
• HT40- High Throughput 40MHz, 802.11n, control channel is bellow extension channel.
• HT40+ High Throughput 40MHz, 802.11n, control channel is above extension channel.
• VHT20 Very High Throughput 20MHz, Supported by 802.11ac
• VHT40 Very High Throughput 40MHz, Supported by 802.11ac
• VHT80 Very High Throughput 80MHz, Supported by 802.11ac
• VHT160 Very High Throughput 160MHz, Supported by 802.11ac
• NOHT disables 11n

The default max channel width VT20 i.e. 20MHz supports a max speed of 150Mbps. Increasing this to 40MHz will increase the maximum theoretical speed to 300Mbps. The catch is that in areas with a lot of Wi-Fi traffic (and Bluetooth etc. which share the same radio frequencies), 40MHz may decrease your overall speed. Devices should detect interference when using 40MHz, and drop back to 20MHz. Edit htmode options in the file /etc/config/wireless and restart the Wi-Fi AP to test various channel widths. Note that option htmode should be set to either HT40+ (for channels 1-7) or HT40- (for channels 5-11) or simply HT40.

In many countries, operating Wi-Fi devices on some or all channels in the 5GHz band requires radar detection and DFS (explanation). If you define a channel in your wireless config that requires DFS according to your country regulations, the 5GHz radio device won’t start up unless the firmware image is able to provide DFS support (i.e. it is both included and enabled). More technical details of the Linux implementation can be found here. DFS works as follows in Linux: The driver detects radar pulses and reports this to nl80211 where the information is processed. If a series of pulses matches one of the defined radar patterns, this will be reported to the user space application (e.g. hostapd) which in turn reacts by switching to another channel.

The following configuration selects channel 104 which needs DFS support as implicitly stated with country code DE:

config	wifi-device		'radio0'
	option	type		'mac80211'
	option	channel		'104'
	option	hwmode		'11a'
	option	path		'pci0000:00/0000:00:00.0'
	option	htmode		'HT20'
	option	country		'DE'
 
config	wifi-iface
	option	device		'radio0'
	option	network		'lan'
	option	mode		'ap'
	option	ssid		'OpenWrt'
	option	encryption	'none'

You can check the country (regulatory domain) your Wi-Fi card thinks it must conform to with

iw reg get

If in doubt, double check your hostapd-phy.conf to make sure it contains the following values, and that your country code is set:

country_code=DE
ieee80211n=1
ieee80211d=1
ieee80211h=1
hw_mode=a

If radar detection is working, DFS channels will show up like this (here for Belgium, iw phy1 info output trimmed):

Frequencies:
* 5220 MHz [44] (17.0 dBm)
* 5240 MHz [48] (17.0 dBm)
* 5260 MHz [52] (20.0 dBm) (radar detection)
DFS state: usable (for 2155257 sec)
DFS CAC time: 60000 ms
* 5280 MHz [56] (20.0 dBm) (radar detection)
DFS state: usable (for 2155257 sec)
DFS CAC time: 60000 ms

When DFS is on, there will be a delay before the interface is enabled (e.g. after reboot). During this time period (often 60 seconds, and determined by local reglations) luci will report the interface is disabled. This time period is used to detect the presence of other signals on the channel (Channel Availability Check Time). This process can be monitored with:

logread -f

If you select a channel that requires DFS in your country and enable HT40, this may result in the DFS start_dfs_cac() failed error (visible with logread):

Configuration file: /var/run/hostapd-phy1.conf
wlan1: interface state UNINITIALIZED->COUNTRY_UPDATE
wlan1: interface state COUNTRY_UPDATE->HT_SCAN
wlan1: interface state HT_SCAN->DFS
wlan1: DFS-CAC-START freq=5680 chan=136 sec_chan=-1, width=0, seg0=0, seg1=0, cac_time=60s
DFS start_dfs_cac() failed, -1
Interface initialization failed
wlan1: interface state DFS->DISABLED
wlan1: AP-DISABLED
hostapd_free_hapd_data: Interface wlan1 wasn't started

Changing your configuration to HT20 should resolve this.