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Is it possible to simultaneously create a single AP on raspberry pi 3 b+ which uses both 2.4 Ghz and 5 Ghz bands so that users with low end devices can connect to the 2.4 Ghz band and users with latest or high end devices can connect to the 5 Ghz band? If so, what is the hostapd for that configuration?

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It is exactly determined what the Raspberry Pi 3B+ is able to do with its WiFi on-board device. With the command iw you can show what interface combinations are possible. Just execute

$ sudo iw list | grep -A4 "valid interface combinations:"
        valid interface combinations:
             * #{ managed } <= 1, #{ P2P-device } <= 1, #{ P2P-client, P2P-GO } <= 1,
               total <= 3, #channels <= 2
             * #{ managed } <= 1, #{ AP } <= 1, #{ P2P-client } <= 1, #{ P2P-device } <= 1,
               total <= 4, #channels <= 1

This means that there are two combinations possible. With the first combination you can setup one (<=1) managed connection (station aka client connection) together with one P2P-device and with a P2P-client, P2P-GO (P2P group owner). This are in total 3 interfaces are usable at the same time. In this combination you can use two #channels (<=2), e.g. a client connection and a P2P-client. The third interface will have the same channel as one of the others.

With the second combination you can setup one (<=1) managed connection (station aka client connection) together with one AP (access point) and with one P2P-client and with one P2P-device. This are in total 4 interfaces are usable at the same time. In this combination you can use one #channels (<=1).

And this is the answer to the question: it is possible to use two channels on different interfaces (first combination) but as far as you use an access point you can only use one channel (second combination).

It is not possible to have an access point on a Raspberry Pi 3B+ which uses both 2.4 Ghz and 5 Ghz bands.

  • very enlightening answer. upvoted indeed – AIOT MAKER May 31 at 20:54
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I believe the chip is unable to hold two channels at once. It should be possible if you add another radio, such as a USB wifi dongle, that would support the other band and channel. You would end up with two network devices.

I would love to be proven wrong, of course, as it would be nice to support both bands.

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I know the OP is almost one year old but I found the OP very interesting and did some research. The Raspberry PI 3B+ uses Cypress SoC CYW43455 for wifi and Bluetooth. The specs of the SoC are impressive but as XTL mentioned earlier this chipset does not support real simultaneous dual-band (RSDB). This is confirmed on this post in Cypress Developer Community.

You will be using Hostapd (Host access point daemon) to build an access point and the specific command used in Hostapd to configure the band is hw_mode and the values to use are "a, b or g" as explained in this other interesting Linux WIFI web page.

  • Thanks for the interesting research, in particular the link to the Cypress Developer Community. But the last comment there is not true for a Raspberry Pi 3B+. You may look at my answer I have just given. – Ingo May 31 at 20:25

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