On 04/04/11 20:16, Gábor Stefanik wrote: > 2011/4/1 Christian Lamparter <chunkeey@xxxxxxxxxxxxxx>: >> On Friday 01 April 2011 18:54:29 Gábor Stefanik wrote: >>> On Fri, Apr 1, 2011 at 9:51 AM, Christian Lamparter >>> <chunkeey@xxxxxxxxxxxxxx> wrote: >>>> On Friday 01 April 2011 05:12:45 Realman Namingston wrote: >>>>> ar9170-based devices record a fair amount of bad packets in monitor >>>>> mode both with the old ar9170usb and new carl9170 drivers. The packets >>>>> contain random BSSIDs, some measure of additional random data, and >>>>> seem to scale proportional to the amount of traffic occurring on the >>>>> observed channel. This behavior makes the devices rather unattractive >>>>> for use in Kismet and site survey applications. >>>>> >>>>> I assume this is due to a shortcoming of the hardware.. but is there >>>>> any potential fix possible? >>>> no, you misunderstood that completely: it's a shortcoming of kismet! >>>> >>>> quote: >>>> "Usually the wireless adapter is unable to transmit in monitor mode and >>>> is restricted to a single wireless channel, though this is dependent on >>>> the wireless adapter's driver, its firmware, and its chip set's features. >>>> Also, in monitor mode the adapter does not check to see if the cyclic >>>> redundancy check (CRC) values are correct for packets captured, so some >>>> captured packets may be corrupted." >>>> >>>> http://en.wikipedia.org/wiki/Monitor_mode >>>> -- >>>> To unsubscribe from this list: send the line "unsubscribe linux-wireless" in >>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>> >>> Isn't ar9170 the wireless-N version of zd1211? Because zd1211 >>> also had this problem with ZD_SNIFFER_ON. See >>> http://patches.aircrack-ng.org/zd1211rw_inject_2.6.26.patch >> inject? ??? > The patch is misnamed. > >> quote from include/net/mac80211.h: >> >> "enum ieee80211_filter_flags - hardware filter flags >> >> These flags determine what the filter in hardware should be >> programmed to let through and what should not be passed to the >> stack. >>>>> It is always safe to pass more frames than requested, >> but this has negative impact on power consumption. <<<<<" >> >> so, if you don't want the garbage then don't enable monitor mode. >> OR set the appropriate FIF_ filter flags and hope the mntr setting >> doesn't affect the way how the hardware/firmware/driver/stack >> marks "bad" frames. > IIRC in zd1211, the garbage was not simply PLCP-failed frames - the HW > returns completely bogus frames with ZD_SNIFFER_ON, even if placed in > an RF isolation chamber. Not sure about ar9170, but AFAIK ar9170 > inherits quite a bit from zd1211. > zd1211 sent garbage constantly, things were actually added to kismet because of that failure. While I personally have no such issues with chr's most excellent driver, I can still point you to kismet's readme and suggest you search for 'fcs'. Assuming the card has a similar issue to the zydas it passes bad frames but validating the fcs drops the bad packets. -Zero_Chaos >> Regards, >> Chr >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
