Dual band

Matthias May matthias.may at neratec.com
Fri Jan 5 15:09:28 PST 2018

On 05/01/18 21:19, Fejes József wrote:
>> Yes this allows you to create 4 APs, but on the same frequency.
>> The key here is not that you can create 4 APs, but the "channels <= 1", meaning the card can only operate on a single
>> frequency.
>> Dual Band usually means the card can operate on 2.4Ghz and 5Ghz, but not at the same time.
>> I'm not aware of "any" card which supports multiple frequencies at the same time, not only from software side, but
>> mainly from hardware side.
>> How would this work? How would you isolate multiple transceivers transmitting at the same time?
>> Scenario:
>> Put 2 different cards into a single device, and put terminators on one, and a power meter on the other:
>> When the card with terminators transmits something, you will still see the signal with ~20dB attenuation on the other card.
>> BR
>> Matthias
> The Asus RT-AC88U router is very similar to the Asus PCE-AC88 card:
> both contain a single BCM4366 chip (they definitely run with the same
> chip firmware). The router can definitely operate in simultaneous dual
> band mode (one channel in the 2.4GHz band and another channel in the
> 5GHz band). The antenna and MIMO configuration also hints at this
> capability. Except the router runs Broadcom's proprietary wl, not
> hostapd.
> Anyway, this part is obsolete for me, as I got a PCE-AC88 for testing,
> but it physically didn't fit in the enclosure of the HP microserver.
> We'll never know if it would have worked or not, my guess is 50-50. My
> plan B is two separate cards in a Mikrotik RB14e so problem solved.
> However, the following still stands: it would be nice if hostapd could
> create and destroy virtual interfaces on demand. It would be somewhat
> similar that I don't have to put the card into AP mode with the iw
> command, hostapd does it for me, and I could create virtual interfaces
> with iw but hostapd could do that too. Then I could run one instance
> of hostapd with two configs, and both configs could reference the same
> physical interface. It's nicer than setting up the virtual interfaces
> by hand and ensuring it happens before hostapd starts.

If you look at the specification of the Asus AP you reference, you will
see that this AP uses internally 2 different cards (See [1]).
When you run a test on this AP where you actually try to use both bands
at 100% you will notice that the two cards interfere with each other.
You will get 100% airtime, but a lot of corrupt frames on both bands.

Regarding your other question:
You can't run multiple hostapd instances on the same physical interface.
What you can do is create multiple virtual interfaces with iw on the
same physical interface which share the hardware (thus the configured
Please read the hostapd.conf example at [2]
Look for the section labeled "Multiple BSSID support"
In such a setup you have a single configuration for a single hostapd
instance but with multiple bssid sections.

Hostapd already has the ability to create virtual interfaces on demand.
Take a look at how wds is handled. For each client a new interface is
dynamically created.

[1] https://wikidevi.com/wiki/ASUS_RT-AC88U
[2] https://w1.fi/cgit/hostap/plain/hostapd/hostapd.conf

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