Dual band

Ben Greear greearb at candelatech.com
Fri Jan 5 15:28:42 PST 2018

On 01/05/2018 03:09 PM, Matthias May wrote:
> 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 Anyway, this part is obsolete for me, as I got a PCE-AC88 for testing,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
> frequency).
> 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.

You can also create multiple virtual interfaces on a single radio, and run a hostapd instance
on each.  You do have to be a bit careful about how you configure things,
and might need to hack hostapd in order to force it to not switch primary/secondary
channels in case where one vdev is HT20 AP and the other is VHT80, for instance.

I am guessing the approach you describe and my approach are effectively
the same in the end...I just find my way easier to support for my particular


Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

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