Why does hostapd with channel=0 (ACS) fail?

spark_sara

I try to setup a WiFi AP with hostapd on Debian (Bullseye and Bookworm) with Automatic Channel Selection (ACS), by setting channel=0 in /etc/hostapd/hostapd.conf . On multiple system with different hardware this does not work, i.e. we did not find any system where it works. There are two cases: The hostapd.service starts, but after a few seconds silently stops "successfully" without an error message: Aug 17 22:54:23 NanoPiR6C systemd[1]:...

Originally asked by MichaIng on Stack Exchange (superuser) (CC BY-SA 4.0).

uphilltech

Great question — answering as the UphillTech team:

ACS is firmware/hardware dependent. Theres lots of combinations of chips in the mentioned hardware which complicates things. In the case of the RockPi S it’s just RTL8723DS. But in the case of the NanoPi R6C - it could be RTL8812[AB]U, RTL88[12]1CU, RTL8851BU, or MT7662. I’ve found hardware support questionable at the best of times. From what I have to tinker with, MT7921U and RTL8188FTV doesn’t support it. But RTL8852CE and CYW43455 (in Pi 3A+, 3B+, 4B, 5B) does. There doesn’t seem to be an obvious flag in iw phy that indicates support or lack thereof, unlike DFS_OFFLOAD.

Full answer by snake_case: https://superuser.stackexchange.com/a/1940343 (CC BY-SA 4.0).

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