Thread: [Madwifi-devel] which kind of frames are observed in monitor mode?
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From: 开. <cai...@gm...> - 2008-05-27 07:12:38
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HI Guys, Thanks so much for your kind assistance and I need further suggestions here: I installed wiresharp in my laptop and can collect data in monitor mode. However, I have something unclear here: 1) Since wireless channel is broadcast, a station tries to receive a frame without the knowledge of its destination. Upon successful reception, if the frame is not destined to him, the wireless card will discard it; 2) There is some probability that a card tried to receive a frame but unfortunately the reception in unsuccessful due to some factors, such as crc error, etc. Then the question is: Will the two kinds of frames described above appear in monitor trace? If so, how to know the further info on whether it was received correctly or not? Answers and suggestions are warmly welcomed. Kai caihong 2008-05-27 |
From: Scott R. <sco...@gm...> - 2008-05-27 07:45:00
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Hi, On 27/05/2008, at 7:12 PM, å¼å½©çº¢ wrote: > > HI Guys, > > Thanks so much for your kind assistance and I need further > suggestions here: > > I installed wiresharp in my laptop and can collect data in monitor > mode. However, I have something unclear here: > > 1) Since wireless channel is broadcast, a station tries to receive a > frame without the knowledge of its destination. Upon successful > reception, if the frame is not destined to him, the wireless card > will discard it; In monitor mode you will receive all frames, regardless of their destination address. No filtering is done by the wireless card. > > 2) There is some probability that a card tried to receive a frame > but unfortunately the reception in unsuccessful due to some factors, > such as crc error, etc. A monitor mode interface will not receive frames with CRC errors by default. You can chose to include these frames with the command: echo 1 > /proc/sys/net/INTERFACE/monitor_crc_errors where INTERFACE is the name of your monitor mode interface, e.g. ath0. > > Then the question is: Will the two kinds of frames described above > appear in monitor trace? If so, how to know the further info on > whether it was received correctly or not? > > The Radiotap header has a flag to indicate whether a received frame failed its CRC. For frames destined for another station, just check the destination address :) > > Answers and suggestions are warmly welcomed. > > > Kai caihong > > 2008-05-27 > > Cheers, -- Scott Raynel WAND Network Research Group Department of Computer Science University of Waikato New Zealand |