3

I'm running hostapd, configured by this project, to create an AP (access point) on an embedded device. I've also tested on a few laptops.

With my laptop, wifi stays connected and a new interface dedicated to the AP is created. On the device, wifi is dropped and the AP is on the standard wifi interface.

The laptop is hostapd v2.4 and bus/pci/drivers/iwlwifi for the driver.

Device is a custom hostapd v0.8.x built for the usb/drivers/r8188eu driver.

It seems to be a hard limitation of the RTL8188 wireless card.

If I want to look at other wireless cards for future devices how can I tell from hardware specifications if it will support connecting and broadcasting at the same time?

Is this "dual-band"? I think some devices can broadcast and connect at once, but only if the AP is broadcast on the same wifi channel, while others can do multi-channel (but it seems r8188eu can do neither).

Then again for all I know the limitation of not being able to connect and broadcast on the same channel could be due to the old version of hostapd.

4
+100

I think you can find the answer to your question in the Arch Linux wiki here: https://wiki.archlinux.org/index.php/software_access_point

This is the relevant section copied from the Arch Linux wiki:


Wi-Fi device must support AP mode You need a nl80211 compatible wireless device, which supports the AP operating mode. This can be verified by running iw list command, under the Supported interface modes block there should be AP listed:

$ iw list
Wiphy phy1
...
    Supported interface modes:
         * IBSS
         * managed
         * AP
         * AP/VLAN
         * WDS
         * monitor
         * mesh point
...

Wireless client and software AP with a single Wi-Fi device Creating a software AP is independent from your own network connection (Ethernet, wireless, ...). Many wireless devices even support simultaneous operation both as AP and as wireless "client" at the same time. Using that capability you can create a software AP acting as a "wireless repeater" for an existing network, using a single wireless device. The capability is listed in the following section in the output of iw list:

$ iw list
Wiphy phy1
...
        valid interface combinations:
                 * #{ managed } <= 2048, #{ AP, mesh point } <= 8, #{ P2P-client, P2P-GO } <= 1,
                   total <= 2048, #channels <= 1, STA/AP BI must match
...

  • Thanks for the extra info, but that is not 100% accurate. My device doesn't support nl80211 yet as I mentioned it is running an AP without issue, though it does not have a dedicated interface as described. – Philip Kirkbride Nov 29 '17 at 22:56
  • 1
    As far as I can tell, the crucial point is the "valid interface combinations". If your card can combine these as described, then it should be able to both access an AP and be an AP at the same time. Although, admittedly, the info shown by iw is very cryptic. I guess the man iw and maybe it's source code will contain more informations. – Tomáš Pospíšek Nov 29 '17 at 23:16
  • My device has iw installed but it can't see my wireless card since it's not nl80211 based. If I use iw wlan1 ... commands I get back No such device (-19). I have to use the old version iwconfig wireless.wiki.kernel.org/en/users/documentation/iw – Philip Kirkbride Nov 29 '17 at 23:21
  • a shot in the dark: maybe you can gather some more info under /sys? – Tomáš Pospíšek Nov 29 '17 at 23:36
  • I won't mark this solved because I don't think it's complete in regards to drivers other than nl80211 but it is good info, so you can have the bounty. – Philip Kirkbride Dec 6 '17 at 16:43

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