Wireless configuration

The wireless 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 is not sufficient).

Sections

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.

Common Options

Name Type RequiredDefault Description
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.
ifname string no (driver default) Specifies a custom name for the wifi interface, which is otherwise automatically named.
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.
channels listno (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
htmode string no (driver default) Specifies the channel width in 802.11n and 802.11ac mode, possible values are: HT20, HT40-, HT40+, HT40, NONE or VHT20, VHT40, VHT80, VHT160
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
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 0Enables 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 supported basic rates. Each basic_rate is measured in kb/s. This option only has an effect on ap and adhoc wifi-ifaces.
supported_rateslist 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. Must be a superset of basic_rate. Basic_rate should be the lowest data rates.
require_mode string no none (AP mode) Set the minimum mode that connecting clients need to support to be allowed to connect. 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 disables 802.11b data rates, 1 enables 802.11b data rates

Broadcom Options

CautionThe options below are only used by the proprietary Broadcom driver (type broadcom).
Name Type RequiredDefault Description
frameburstbooleanno 0 Enables Broadcom frame bursting if supported
maxassoc integerno (driver default)Limits the maximum allowed number of associated clients
slottime integerno (driver default)Slot time in milliseconds

Ubiquity Nanostation Options

CautionThe options below are only used by the Ubiquity Nanostation family of devices
Name Type RequiredDefault Description
antennastringno (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:

  • 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 wifi 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

Common Options

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

Name Type RequiredDefault Description
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 LEDE 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.
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, wep+open, wep+mixed to focre 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. 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 addressesno (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). Not supported by all drivers
ieee80211w_max_timeout integer no (hostapd default) Specifies the 802.11w Association SA Query maximum timeout.
ieee80211w_retry_timeoutinteger 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 wifi interface.
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 mode
wds boolean no 0 This sets 4-address mode

WPA Modes

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.

Value WPA Version Ciphers
psk2+tkip+ccmp WPA2 Personal (PSK) TKIP, CCMP
psk2+tkip+aes WPA2 Personal (PSK) TKIP, AES
psk2+tkip WPA2 Personal (PSK) TKIP
psk2+ccmp WPA2 Personal (PSK) CCMP
psk2+aes WPA2 Personal (PSK) AES
psk2 WPA2 Personal (PSK)
psk+tkip+ccmp WPA Personal (PSK) TKIP, CCMP
psk+tkip+aes WPA Personal (PSK) TKIP, AES
psk+tkip WPA Personal (PSK) TKIP
psk+ccmp WPA Personal (PSK) CCMP
psk+aes WPA Personal (PSK) AES
psk WPA Personal (PSK)
psk-mixed+tkip+ccmpWPA/WPA2 Personal (PSK) mixed modeTKIP, CCMP
psk-mixed+tkip+aes WPA/WPA2 Personal (PSK) mixed modeTKIP, AES
psk-mixed+tkip WPA/WPA2 Personal (PSK) mixed modeTKIP
psk-mixed+ccmp WPA/WPA2 Personal (PSK) mixed modeCCMP
psk-mixed+aes WPA/WPA2 Personal (PSK) mixed modeAES
psk-mixed WPA/WPA2 Personal (PSK) mixed mode
wpa2+tkip+ccmp WPA2 Enterprise TKIP, CCMP
wpa2+tkip+aes WPA2 Enterprise TKIP, AES
wpa2+ccmp WPA2 Enterprise CCMP
wpa2+aes' WPA2 Enterprise AES
wpa2 WPA2 Enterprise
wpa2+tkip WPA2 Enterprise TKIP
wpa+tkip+ccmp WPA Enterprise TKIP, CCMP
wpa+tkip+aes WPA Enterprise TKIP, AES
wpa+ccmp WPA Enterprise CCMP
wpa+aes WPA Enterprise ES
wpa+tkip WPA Enterprise TKIP
wpa WPA Enterprise
wpa-mixed+tkip+ccmpWPA/WPA2 Enterprise mixed mode TKIP, CCMP
wpa-mixed+tkip+aes WPA/WPA2 Enterprise mixed mode TKIP, AES
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 AES
wpa-mixed WPA/WPA2 Enterprise mixed mode

WPA Enterprise (Access Point)

Listing of Access Point related options for WPA Enterprise.

Name Default Description
server (none)RADIUS server to handle client authentication
port 1812 RADIUS port
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_naming 1 VLAN Naming
vlan_tagged_interface(none)VLAN Tagged Interface
vlan_bridge (none)VLAN Bridge Naming Scheme - added in https://dev.openwrt.org/changeset/43473/

WPA Enterprise (Client)

Listing of Client related options for WPA Enterprise.

Name Default Description
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
CautionWhen 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'

WPA Key Reinstallation Attack workaround

Name Default Description
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

WPS Options

Listing of Wi-Fi Protected Setup related options.

CautionSupport for WPS is provided by packages wpad and hostapd-utils. Default package wpad-mini is not enough.
CautionWPS is possible only when encryption PSK/PSK2 is selected.
Name Type RequiredDefault Description
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 booleanno 0 Enable label configuration method.
wps_manufacturerstring no lede-project.orgThe manufacturer of the device (up to 64 ASCII characters).
wps_pushbutton booleanno 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:

  • 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

/etc/config/wireless example fie required for better understanding like below

root@XYZ:~# cat /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'
root@XYZ:~#

Fast BSS transition Options

Name Type RequiredDefault Description
ieee80211r booleanno 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 integerno 10000 Default lifetime of the PMK-RO in minutes [1-65535].
r1_key_holder string no 00004f577274PMK-R1 Key Holder identifier (dot11FTR1KeyHolderID). A 6-octet identifier as a hex string.
reassociation_deadlineintegerno 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 booleanno 0 Whether PMK-R1 push is enabled at R0KH.
ft_over_ds booleanno 1 Whether to enable FT-over-DS.
ft_psk_generate_local booleanno 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.

Inactivity Timeout Options

Name Type RequiredDefault Description
disassoc_low_ack booleanno 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 integerno 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_pollbooleanno 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 integerno 65535Maximum allowed Listen Interval (how many Beacon periods STAs are allowed to remain asleep).

Start/Stop Wireless

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.

Regenerate Configuration

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

40 MHz channel width (up to 300 Mbps) for 802.11n devices ONLY

The default max channel width of 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 wifi 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 wifi 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.

DFS / Radar Detection

In many countries, operating WiFi 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     lede
	option encryption none

You can check the country (regulatory domain) your WiFi 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
CautionWhen 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.