The wireless radio UCI configuration is located in /etc/config/wireless.
If the device has ethernet ports, the wireless is turned OFF by default.
You can turn it on in
/etc/config/wireless by changing
option disabled '1' to
option disabled '0' (commenting out the line or removing it is sufficient).
A typical wireless config file contains at least a pair of:
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'
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.
|type||string||yes||(autodetected)||The type is determined on firstboot during the initial radio device detection - it is usually not required to change it. Used values are broadcom on brcm47xx, or mac80211 for all other platforms|
|phy||string||no/yes||(autodetected)||Specifies the radio phy associated to this section. If present, it is usually autodetected and should not be changed.|
|macaddr||MAC address||yes/no||(autodetected)||Specifies the radio adapter associated to this section, it is not used to change the device mac but to identify the underlying interface.|
|disabled||boolean||no||0||Disables the radio adapter if set to 1. Removing this option or setting it to 0 will enable the adapter|
|channel||integer or “auto”||yes||auto||Specifies the wireless channel to use. “auto” defaults to the lowest available channel, or utilizes the ACS algorithm depending on hardware/driver support.|
|channels||list||no||(regulatory domain specific)||Use specific channels, when channel is in “auto” mode. This option allows hostapd to select one of the provided channels when a channel should be automatically selected. Channels can be provided as range using hyphen ('-') or individual channels can be specified by space (' ') separated values.|
|hwmode||string||no||(driver default)||Selects the wireless protocol to use, possible values are 11b, 11g, and 11a. Note that 11ng and 11na are not available options, see ticket 17541.|
|htmode||string||no||(driver default)||Specifies the channel width in 802.11n and 802.11ac mode. See this section for details. Possible values are: HT20, HT40-, HT40+, HT40, or VHT20, VHT40, VHT80, VHT160, NOHT disables 11n|
|chanbw||integer||no||20||Specifies a narrow channel width in MHz, possible values are: 5, 10, 20|
|ht_capab||string||no||(driver default)||Specifies the available capabilities of the radio. The values are autodetected. See here for options (check vs. the version of hostapd installed on your router using the “refs” link)|
|txpower||integer||no||(driver default)||Specifies the transmission power in dBm|
|diversity||boolean||no||1||Enables or disables the automatic antenna selection by the driver|
|rxantenna||integer||no||(driver default)||Specifies the antenna for receiving, the value may be driver specific, usually it is 1 for the first and 2 for the second antenna. Specifying 0 enables automatic selection by the driver if supported. This option has no effect if diversity is enabled|
|txantenna||integer||no||(driver default)||Specifies the antenna for transmitting, values are identical to rxantenna|
|country||varies||no||(driver default)||Specifies the country code, affects the available channels and transmission powers. For type broadcom a two letter country code is used (EN or DE). The madwifi driver expects a numeric code.|
|country_ie||boolean||no||1 if country is set, otherwise 0||Enables IEEE 802.11d country IE (information element) advertisement in beacon and probe response frames. This IE contains the country code and channel/power map. Requires country.|
|distance||integer||no||(driver default)||Distance between the ap and the furthest client in meters.|
|beacon_int||integer||no||100 (hostapd default)||Set the beacon interval. This is the time interval between beacon frames, measured in units of 1.024 ms. hostapd permits this to be set between 15 and 65535. This option only has an effect on ap and adhoc wifi-ifaces|
|basic_rate||list||no||(hostapd/driver default)||Set the basic data rates. Each basic_rate is measured in kb/s. This option only has an effect on ap and adhoc wifi-ifaces.|
|supported_rates||list||no||(hostapd/driver default)||Set the supported data rates. Each supported rate is measured in kb/s. This option only has an effect on ap and adhoc wifi-ifaces. This must be a superset of the rates set in basic_rate. The minimum basic rate should also be the minimum supported rate.|
|require_mode||string||no||none||(AP mode) Set the minimum mode that connecting clients need to support to be allowed to connect and overrides legacy_rates to 0 to disable legacy 802.11b data rates. Supported values: g = 802.11g, n = 802.11n, ac = 802.11ac|
|log_level||integer||no||2||Set the log_level. Supported levels are: 0 = Verbose Debugging, 1 = Debugging, 2 = Informational Messages, 3 = Notification, 4 = Warning|
|legacy_rates||boolean||no||1||0 = Disable legacy 802.11b data rates, 1 = Enable legacy 802.11b data rates. basic_rate and supported_rates overrides this option.|
|cell_density||integer||no||0||Configures data rates based on the coverage cell density. Normal configures basic rates to 6, 12, 24 Mbps if legacy_rates is 0, else to 5.5, 11 Mbps. High configures basic rates to 12, 24 Mbps if legacy_rates is 0, else to the 11 Mbps rate. Very High configures 24 Mbps as the basic rate. Supported rates lower than the minimum basic rate are not offered. basic_rate and supported_rates overrides this option. 0 = Disabled, 1 = Normal, 2 = High, 3 = Very High|
The options below are only used by the proprietary Broadcom driver (type broadcom).
|frameburst||boolean||no||0||Enables Broadcom frame bursting if supported|
|maxassoc||integer||no||(driver default)||Limits the maximum allowed number of associated clients|
|slottime||integer||no||(driver default)||Slot time in milliseconds|
The options below are only used by the Ubiquity Nanostation family of devices.
|antenna||string||no||(driver default)||Selects the antenna, possible values are vertical for internal vertical polarization, horizontal for internal horizontal polarization or external to use the external antenna connector|
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:
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'
The common configuration option for wifi-iface sections are listed below.
|ifname||string||no||(driver default)||Specifies a custom name for the Wi-Fi interface, which is otherwise automatically named. Maximum length: 15 characters (See Network Basics for more info)|
|device||string||yes||(first device id)||Specifies the used wireless adapter, must refer to one of the defined wifi-device sections|
|network||string||yes||lan||Specifies the network interface to attach the wireless to.|
|mode||string||yes||ap||Selects the operation mode of the wireless network interface controller. Possible values are ap, sta, adhoc, wds, monitor, mesh|
|disabled||boolean||no||0||When set to 1, wireless network is disabled.|
|ssid||string||yes||OpenWrt||The broadcasted SSID of the wireless network and for for managed mode the SSID of the network you’re connecting to|
|bssid||BSSID address||no||(driver default)||Override the BSSID of the network, only applicable in adhoc or sta mode. In wds mode specifies the BSSID of another AP to create WDS with.|
|mesh_id||Mesh ID||no||none||The Mesh ID as defined in IEEE 802.11s. If set, the wireless interface will join this mesh network when brought up. If not, it is necessary to invoke iw <iface> mesh join <mesh_id> to join a mesh after the interface is brought up.|
|hidden||boolean||no||0||Turns off SSID broadcasting if set to 1|
|isolate||boolean||no||0||Isolate wireless clients from each other, only applicable in ap mode. See this post for details.|
|doth||boolean||no||0||Enables 802.11h support.|
|wmm||boolean||no||1||Enables WMM (802.11e) support. Required for 802.11n support|
|encryption||string||no||none||Wireless encryption method. Possible values are: none, wep, psk, psk2. For WEP station mode the default is “open system” authentication. Use wep+shared or wep+open to force a specific mode.|
|key||integer or string||no||(none)||In any WPA-PSK mode, this is a string that specifies the pre-shared passphrase from which the pre-shared key will be derived. The clear text key has to be 8-63 characters long. If a 64-character hexadecimal string is supplied, it will be used directly as the pre-shared key instead. In WEP mode, this can be an integer specifying which key index to use (key1, key2, key3, or key4.) Alternatively, it can be a string specifying a passphrase or key directly, as in key1. In any WPA-Enterprise AP mode, this option has a different interpretation.|
|key1||string||no||(none)||WEP passphrase or key #1 (selected by the index in key). This string is treated as a passphrase from which the WEP key will be derived. If a 10- or 26-character hexadecimal string is supplied, it will be used directly as the WEP key instead.|
|key2||string||no||(none)||WEP passphrase or key #2 (selected by the index in key), as in key1.|
|key3||string||no||(none)||WEP passphrase or key #3 (selected by the index in key), as in key1.|
|key4||string||no||(none)||WEP passphrase or key #4 (selected by the index in key), as in key1.|
|macfilter||string||no||disable||Specifies the mac filter policy, disable to disable the filter, allow to treat it as whitelist or deny to treat it as blacklist.|
|maclist||list of MAC addresses||no||(none)||List of MAC addresses (divided by spaces) to put into the mac filter.|
|iapp_interface||string||no||(none)||Specifies a network interface to be used for 802.11f (IAPP) - only enabled when defined.|
|rsn_preauth||boolean||no||0||Allow preauthentication for WPA2-EAP networks (and advertise it in WLAN beacons). Only works if the specified network interface is a bridge.|
|ieee80211w||integer||no||0||Enables MFP (802.11w) support (0 = disabled, 1 = optional, 2 = required). Requires the 'full' version of wpad/hostapd and support from the Wi-Fi driver|
|ieee80211w_max_timeout||integer||no||(hostapd default)||Specifies the 802.11w Association SA Query maximum timeout.|
|ieee80211w_retry_timeout||integer||no||(hostapd default)||Specifies the 802.11w Association SA Query retry timeout.|
|maxassoc||integer||no||(hostapd/driver default)||Specifies the maximum number of clients to connect.|
|macaddr||mac address||no||(hostapd/driver default)||Overrides the MAC address used for the Wi-Fi interface. Warning: if the MAC address specified is a multicast address, this override will fail silently. To avoid this problem, ensure that the mac address specified is a valid unicast mac address.|
|dtim_period||integer||no||2 (hostapd default)||Set the DTIM (delivery traffic information message) period. There will be one DTIM per this many beacon frames. This may be set between 1 and 255. This option only has an effect on ap wifi-ifaces.|
|short_preamble||boolean||no||1||Set optional use of short preamble|
|max_listen_int||integer||no||65535 (hostapd default)||Set the maximum allowed STA (client) listen interval. Association will be refused if a STA attempts to associate with a listen interval greater than this value. This option only has an effect on ap wifi-ifaces.|
|mcast_rate||integer||no||(driver default)||Sets the fixed multicast rate, measured in kb/s. Only supported in adhoc and mesh modes|
|wds||boolean||no||0||This sets 4-address mode|
|owe_transition_ssid||string||no||none||Opportunistic Wireless Encryption (OWE) Transition SSID (only for OPEN and OWE networks)|
|owe_transition_bssid||BSSID address||no||none||Opportunistic Wireless Encryption (OWE) Transition BSSID (only for OPEN and OWE networks)|
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
To use the WPA3 modes as station (client), it is required to install the
To support both access point and station modes with WPA3, it is possible to install the
|Value||WPA Version||Ciphers||Supported since|
|sae||WPA3 Personal (SAE)||CCMP||19.07|
|sae-mixed||WPA2/WPA3 Personal (PSK/SAE) mixed mode||CCMP||19.07|
|psk2+tkip+ccmp||WPA2 Personal (PSK)||TKIP, CCMP|
|psk2+tkip+aes||WPA2 Personal (PSK)||TKIP, CCMP|
|psk2+tkip||WPA2 Personal (PSK)||TKIP|
|psk2+ccmp||WPA2 Personal (PSK)||CCMP|
|psk2+aes||WPA2 Personal (PSK)||CCMP|
|psk2||WPA2 Personal (PSK)||CCMP|
|psk+tkip+ccmp||WPA Personal (PSK)||TKIP, CCMP|
|psk+tkip+aes||WPA Personal (PSK)||TKIP, CCMP|
|psk+tkip||WPA Personal (PSK)||TKIP|
|psk+ccmp||WPA Personal (PSK)||CCMP|
|psk+aes||WPA Personal (PSK)||CCMP|
|psk||WPA Personal (PSK)||CCMP|
|psk-mixed+tkip+ccmp||WPA/WPA2 Personal (PSK) mixed mode||TKIP, CCMP|
|psk-mixed+tkip+aes||WPA/WPA2 Personal (PSK) mixed mode||TKIP, CCMP|
|psk-mixed+tkip||WPA/WPA2 Personal (PSK) mixed mode||TKIP|
|psk-mixed+ccmp||WPA/WPA2 Personal (PSK) mixed mode||CCMP|
|psk-mixed+aes||WPA/WPA2 Personal (PSK) mixed mode||CCMP|
|psk-mixed||WPA/WPA2 Personal (PSK) mixed mode||CCMP|
|wpa2+tkip+ccmp||WPA2 Enterprise||TKIP, CCMP|
|wpa2+tkip+aes||WPA2 Enterprise||TKIP, CCMP|
|wpa+tkip+ccmp||WPA Enterprise||TKIP, CCMP|
|wpa+tkip+aes||WPA Enterprise||TKIP, AES|
|wpa-mixed+tkip+ccmp||WPA/WPA2 Enterprise mixed mode||TKIP, CCMP|
|wpa-mixed+tkip+aes||WPA/WPA2 Enterprise mixed mode||TKIP, CCMP|
|wpa-mixed+tkip||WPA/WPA2 Enterprise mixed mode||TKIP|
|wpa-mixed+ccmp||WPA/WPA2 Enterprise mixed mode||CCMP|
|wpa-mixed+aes||WPA/WPA2 Enterprise mixed mode||CCMP|
|wpa-mixed||WPA/WPA2 Enterprise mixed mode||CCMP|
|owe||Opportunistic Wireless Encryption (OWE)||CCMP||19.07|
Listing of Access Point related options for WPA Enterprise.
|server||(none)||RADIUS server to handle client authentication|
|key||(none)||Shared RADIUS secret|
|wpa_group_rekey||600||WPA Group Cipher rekeying interval in seconds|
|auth_server||(none)||RADIUS authentication server to handle client authentication|
|auth_port||1812||RADIUS authentication port|
|auth_secret||(none)||Shared authentication RADIUS secret|
|auth_cache||0||Disable or enable PMKSA and Opportunistic Key Caching|
|acct_server||(none)||RADIUS accounting server to handle client authentication|
|acct_port||1813||RADIUS accounting port|
|acct_secret||(none)||Shared accounting RADIUS secret|
|nasid||(none)||NAS ID to use for RADIUS authentication requests|
|ownip||(none)||NAS IP Address to use for RADIUS authentication requests|
|dae_client||(none)||Dynamic Authorization Extension client. This client can send “Disconnect-Request” or “CoA-Request” packets to forcibly disconnect a client or change connection parameters.|
|dae_port||3799||Port the Dynamic Authorization Extension server listens on.|
|dae_secret||(none)||Shared DAE secret.|
|dynamic_vlan||0||Dynamic VLAN assignment|
|vlan_tagged_interface||(none)||VLAN Tagged Interface|
|vlan_bridge||(none)||VLAN Bridge Naming Scheme - added in https://dev.openwrt.org/changeset/43473/|
Listing of Client related options for WPA Enterprise.
|eap_type||(none)||Defines the EAP protocol to use, possible values are tls for EAP-TLS and peap or ttls for EAP-PEAP|
|auth||MSCHAPV2||“auth=PAP”/PAP/MSCHAPV2 - Defines the phase 2 (inner) authentication method to use, only applicable if eap_type is peap or ttls|
|identity||(none)||EAP identity to send during authentication|
|password||(none)||Password to send during EAP authentication|
|ca_cert||(none)||Specifies the path the CA certificate used for authentication|
|client_cert||(none)||Specifies the client certificate used for the authentication|
|priv_key||(none)||Specifies the path to the private key file used for authentication, only applicable if eap_type is set to tls|
|priv_key_pwd||(none)||Password to unlock the private key file, only works in conjunction with priv_key|
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'
option auth 'auth=PAP'
|wpa_disable_eapol_key_retries||0||Workaround for key reinstallation attacks (requires LEDE 17.01.4 or higher)|
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:
|tdls_prohibit||0||Prohibit the use of TDLS on the network (complicates key reinstallation attacks against TDLS) (requires hostapd/wpad 2016-12-19-ad02e79d-7 or higher)|
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.
|wps_config||list||no||(none)||List of configuration methods. Currentlly supported methods are: push_button.|
|wps_device_name||string||no||LEDE AP||User-friendly description of device; up to 32 octets encoded in UTF-8.|
|wps_device_type||string||no||6-0050F204-1||Primary device type. Examples: 1-0050F204-1 (Computer / PC), 1-0050F204-2 (Computer / Server), 5-0050F204-1 (Storage / NAS), 6-0050F204-1 (Network Infrastructure / AP)|
|wps_label||boolean||no||0||Enable label configuration method.|
|wps_manufacturer||string||no||lede-project.org||The manufacturer of the device (up to 64 ASCII characters).|
|wps_pushbutton||boolean||no||0||Enable push-button configuration method.|
|wps_pin||string||no||none||The PIN to use with WPS-PIN (only in external registrar mode?)|
Minimal steps needed to get WPS running:
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):
When using WPS-PIN:
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
# /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'
|ieee80211v||boolean||no||0||Enables BSS transition (802.11v) support.|
|time_advertisement||integer||no||0||Time advertisement. 0 is disabled (see hostapd's time_advertisement setting).|
|wnm_sleep_mode||boolean||no||0||WNM-Sleep Mode (extended sleep mode for stations).|
|bss_transition||boolean||no||0||BSS Transition Management.|
|ieee80211r||boolean||no||0||Enables fast BSS transition (802.11r) support.|
|nasid||string||yes||(none)||PMK-R0 Key Holder identifier (dot11FTR0KeyHolderID). A 1 to 48 octet identifier.|
|mobility_domain||string||no||4f57||Mobility Domain identifier (dot11FTMobilityDomainID, MDID). MDID is used to indicate a group of APs (within an ESS, i.e., sharing the same SSID) between which a STA can use Fast BSS Transition. 2-octet identifier as a hex string.|
|r0_key_lifetime||integer||no||10000||Default lifetime of the PMK-RO in minutes [1-65535].|
|r1_key_holder||string||no||00004f577274||PMK-R1 Key Holder identifier (dot11FTR1KeyHolderID). A 6-octet identifier as a hex string.|
|reassociation_deadline||integer||no||1000||Reassociation deadline in time units (TUs / 1.024 ms, 1000-65535)|
|r0kh||string||no||(none)||List of R0KHs in the same Mobility Domain. Valid format: <MAC address>,<NAS Identifier>,<128-bit key as hex string> This list is used to map R0KH-ID (NAS Identifier) to a destination MAC address when requesting PMK-R1 key from the R0KH that the STA used during the Initial Mobility Domain Association.|
|r1kh||string||no||(none)||List of R1KHs in the same Mobility Domain. Valid format: <MAC address>,<R1KH-ID>,<128-bit key as hex string> This list is used to map R1KH-ID to a destination MAC address when sending PMK-R1 key from the R0KH. This is also the list of authorized R1KHs in the MD that can request PMK-R1 keys.|
|pmk_r1_push||boolean||no||0||Whether PMK-R1 push is enabled at R0KH.|
|ft_over_ds||boolean||no||1||Whether to enable FT-over-DS.|
|ft_psk_generate_local||boolean||no||0||Whether to generate FT response locally for PSK networks. This avoids use of PMK-R1 push/pull from other APs with FT-PSK networks as the required information (PSK and other session data) is already locally available.|
|disassoc_low_ack||boolean||no||1||Disassociate stations based on excessive transmission failures or other indications of connection loss. This depends on the driver capabilities and may not be available with all drivers.|
|max_inactivity||integer||no||300||Station inactivity limit in seconds: If a station does not send anything in ap_max_inactivity seconds, an empty data frame is sent to it in order to verify whether it is still in range. If this frame is not ACKed, the station will be disassociated and then deauthenticated.|
|skip_inactivity_poll||boolean||no||0||The inactivity polling can be disabled to disconnect stations based on inactivity timeout so that idle stations are more likely to be disconnected even if they are still in range of the AP.|
|max_listen_interval||integer||no||65535||Maximum allowed Listen Interval (how many Beacon periods STAs are allowed to remain asleep).|
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
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.
HT20High Throughput 20MHz, 802.11n
HT40High 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.
VHT20Very High Throughput 20MHz, Supported by 802.11ac
VHT40Very High Throughput 40MHz, Supported by 802.11ac
VHT80Very High Throughput 80MHz, Supported by 802.11ac
VHT160Very High Throughput 160MHz, Supported by 802.11ac
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.
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
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  (17.0 dBm) * 5240 MHz  (17.0 dBm) * 5260 MHz  (20.0 dBm) (radar detection) DFS state: usable (for 2155257 sec) DFS CAC time: 60000 ms * 5280 MHz  (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:
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.