5GHz SSID don't show up when using certain channels on vht40/80

Hi all,

When using these settings:

htmode: vht40
channel: 40


htmode: vht80
channel: 44

5Ghz SSID's do not show up, even though wlan0 is up (ifconfig) and I get these errors:

daemon.err hostapd: Failed to set beacon parameters
daemon.notice hostapd: handle_probe_req: send failed
config wifi-device 'radio0'
    option type 'mac80211'
    option hwmode '11a'
    option path 'pci0000:00/0000:00:00.0'
    option disabled '0'
    option distance '30'
    option country 'US'
    option htmode 'VHT40'
    option noscan '0'
    option channel '40'
    option txpower '28'

It starts working when I change the channel to 44 or 36. I am in the US.

Any advice?

Not all channels in the 5 GHz band are "equal" in that some are under DFS restrictions and you can't "start" a 40, 80, or 160 MHz bandwidth channel "anywhere". With DFS, you'll be pushed out of the DFS region as soon as there is a detection of radar in operation (which could be many miles away from you). I don't recall exactly how hostapd numbers wider channels, but you may have to play a bit with the "base" channel number.

1 Like

The article linked by @jeff explains the channel allocation (for the USA) really well. It ends up that there are two valid non-DFS 80 MHz channels: 42 and 155. 42 covers up the entire lower non-DFS band, and 155 uses the higher non-DFS band except for channel 165, where 20 MHz operation is possible.

@jeff thanks for a great article. helped me understand channels much better.
@mk24 yep. now I understand widths and allocation.

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