WiFi Beacon Packets

Question

I'm trying to write a simple C code with WinPcap to broadcast a beacon packet and capture it in all nearby WiFi units. The code I'm using is very similar to the ones available at WinPcap[1].

The code runs fine if I create an ad-hoc network connection and join all the computers into it. However, this process of creating and joining to an ad-hoc network is cumbersome. It would be much better if, regardless of what network each computer is in, the beacon packets would be broadcasted and captured once the code is running.

As simple as this problem might sound, after some searching it seems that this is not possible to be done on windows (unless re-writing drivers or maybe the kernel):

• Raw WiFi Packets with WinPcap[2]
• Sending packets without network connection[3]
• Does winpcap/libpcap allow me to send raw wireless packets?[4]

Basically, it would be necessary to use the WiFi in monitor mode, which is not supported in Windows[5]. Therefore, if the computers are not in the same network connection, the packets will be discarded.

1st Issue
I'm still intriguing, beacon and probe request packets are a normal traffic across the network. How they could be being sent and received constantly but the user is not allowed to write a program to do so? How to reconcile that?

2nd Issue
Does anyone has experience with Managed Wifi API[6]? I've heard that it might help.

3rd Issue
Acrylic WiFi[7] claims to have developed a NDIS driver which support monitor mode under Windows. Does anyone has experience with this software? Is it possible to integrate with C codes?

4th Issue
Is it possible to code such Wifi beacon on Linux? and on Android?

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1. www.winpcap.org/docs/docs_412/html/main.html
2. stackoverflow.com/questions/34454592/raw-wifi-packets-with-winpcap/34461313?noredirect=1#comment56674673_34461313
3. stackoverflow.com/questions/25631060/sending-packets-without-network-connection-wireless-adapter
4. stackoverflow.com/questions/7946497/does-winpcap-libpcap-allow-me-to-send-raw-wireless-packets
5. en.wikipedia.org/wiki/Monitor_mode#Operating_system_support
6. managedwifi.codeplex.com/
7. www.acrylicwifi.com/

Answer 1

Couple questions I will try to answer. Mgmt and Ctrl packets are used for running a wifi network and don't contain data, I would not call these normal packets. Windows used to(I think still does) convert data packets into ethernet frames and pass it up the stack. Beacon and Probe Req pkts are not necessary for TCP/IP stack to work, ie. web browsers don't need beacon frames to get your web page. Most OS's need minimal info from mgmt/ctrl pkts to help a user interact with a wifi adapter, most mgmt/ctrl pkts only are useful to the driver(and low level os components) to figure how to interact with the network. This way the wifi adapters look and act like ethernet adapters to high level os components.

Never had any experience with Managed Wifi API or Acrylic, so can't give you any feedback.

Most analyzers that capture and send packets do it in 2-3 separate modes mainly because of hardware. Wifi adapters can be in listen mode(promiscuous mode and/or monitor mode) or adapter mode. To capture network traffic you need to listen and not send, ie. if someone sends a pkt while you are sending you miss that traffic. In order to capture(or send) traffic you will need a custom NDIS driver in windows, on linux many of them already do. Checkout wireshark or tshark, they use winpcap to capture pkts in windows and there are some adapters they recommend to use to capture pkts.

Yes it is possible to send a beacon on linux, ie. Aireplay. I know its possible to capture traffic on Android but you it needs to have rooted or custom firmware, which I would believe also means you can send custom pkts. If you are simply trying to send a pkt it might be easier to capture some traffic in tshark or wireshark and use something like aireplay to resend that traffic. You could also edit the packet with a hex editor to tune it to what you need.