When I was recently on business travel, I used my smartphone for Wi-Fi tethering my notebook to the Internet over the 6 GHz band. But every now and then, my notebook wouldn’t find the smartphone’s network and I had to switch to the 5 GHz band to make it work again. After a bit of back and forth between the two bands over a couple of days I noticed a pattern.
The pattern was actually quite simple: Whenever I returned to the hotel in the evening, my computer failed to detect the Wi-Fi network in the 6 GHz band. The next morning, back at the meeting location, it was suddenly working again. So why was that?
As 6 GHz is not yet approved for use in all countries, Intel has some sort of detection algorithm in the Wi-Fi chip’s firmware that tries to find out if the 6 GHz band can be used. I suspect, but can’t be entirely certain, that the chip looks at the country IDs of access points it can detect. So could that be the reason for the notebook not finding the network? Here’s a Linux command to check this:
iw list | grep "5975"
‘5975’ is the frequency of the second channel of the 6 GHz band and the command gave me the following result when the network could not be detected:
5975 MHz [5] (disabled)
And later at the meeting location, the band was enabled again:
5975 MHz [5] (22.0 dBm) (no IR)
So this proves that the network was not found because the Wi-Fi chip disabled the 6 GHz band every time I opened the notebook at the hotel. So how about the country ID theory? Here’s a shell command that lists the country IDs that can be found during a network scan and what it found at the hotel:
sudo iw dev wlp0s20f3 scan | grep -B4 "Country"
Apart from many ES (Spain) and EU (European Union) country IDs, there was one Access Point with a country id from Indonesia and one from Chile. While Chile has opened the 6 GHz band for Wi-Fi according to the Wi-Fi Alliance’s current country list, Indonesia has not. So I suspect that the country id of this access point was the reason.
But the story doesn’t end here. I was hoping that as soon as that access point would go away, the Wi-Fi chip would enable the 6 GHz band again. Unfortunately, there seems to be a delay timer that keeps blocking the band for 30 to 45 minutes after the last occurrence of a non-supporting country id.
In other words, it is quite simple to disable the 6 GHz band at a location with a wrongly or maliciously configured access point. Bummer…