Hostapd recognizing ACKs from wpa_supplicant, but not external stations nor a packet crafter immediately adjacent to hostapd's interfaces

Alfred Kenny alfred.kenny at
Thu May 28 13:26:54 EDT 2015

I appreciate the replies thus far, but -- before this goes any further -- I should mention that I 
am really quite the amateur when it comes to working with hardware, firmware and drivers. 
I've been looking for documentation that spells things out in detail for hostapd, mac80211_hwsim,
associated drivers and their interaction, but it seems like I need to have a bachelors in computer/software 
engineering (rather than my lowly electrical degree) to fully understand what's going on. 
So, I apologize if it'll be frustrating, but I'd be grateful if you could imagine that I'm a 15 year 
old who is interested in working with the open-source software and hardware components 
involved in 802.11 wireless communications. 

This is the setup for our system, with each component shown existing on a linux machine:

That is to say, at no point does a wireless card come into play. All wireless transmissions are 
handled by a WARP board which is listening for ethernet packets that have been placed on the 
PC's eth1 and forwarding all relevant packets from the air back to the eth1.

There, now that that huge preamble is complete, let's get to the points you've made.

> You will need to sniff with a second radio that is only acting as sniffer
> if you want to see all frames on the air (from other radios).

Do you mean that I need to use a wireless card for the sole purpose of recognizing 
ACKs directed toward this network? We're attempting to operate several networks 
simultaneously with our setup, with each using a dedicated wlan interface. How would
this work in such a configuration?

> And some drivers/firmware, such as ath10k, still has issues sniffing certain packets.
> ath9k (a/b/g/n) is a very good sniffer, and definitely shows beacons and such.

Can these drivers somehow be operated independently of our system without 
additional hardware? Remember that our system functions without the use of a wireless
card. In fact, you could strip every networking device from the linux machine except for
the ethernet card (eth1) and motherboard (eth0) and everything would function exactly
as it does now.

> As far as I know, no ACK frames are actually handed up the stack for any real driver.  The firmware and/or
> hardware consumes them.  The tx-status often indicates whether ACK happened or not, however.

Where would we be able to see this tx-status on the linux machine? Or is this only produced when 
a wireless card is in place for receiving frames from air? When we run our system exactly as is with
hostapd and mac80211_hwsim and then use wpa_supplicant as a test station, its ACKs are only seen
at hwsim0 and apparently hostapd has been notified that they were received. This seems incongruous
with the above point.

Thanks again for all the replies. This is still mostly greek to me at this point. If anyone has any
comprehensive documentation with test examples for the components that have been mentioned 
thus far, I'd be more than happy to pore over them rather than bothering all of you.


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