Re: [Madwifi-devel] Radiotap and FCS bytes
Status: Beta
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From: Pavel R. <pr...@gn...> - 2007-03-24 15:03:25
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Quoting Scott Raynel <sco...@gm...>: > Hi all, > > I'd like to start a discussion on how the FCS bytes should be handled > on received frames in monitor mode. The data we know and can pass to the userspace should be passed. And we should follow the standard. > The reason for starting this discussion is that David Young (the > Radiotap maintainer) recently modified our wiki page on Radiotap to > remove the reference to IEEE80211_RADIOTAP_FCS, as it is not part of > the standard (and it appears that many people use our wiki page as a > reference for Radiotap). What's worse, IEEE80211_RADIOTAP_FCS made it into Linux headers. Yet it's quite pointless to pass the checksum in the header if there is a natural place for it in the frame itself. > MadWiFi's Radiotap implementation currently > use this non-standard field to record the FCS bytes for each frame > before removing them from the end of the packet. Bad, bad, bad. > I'd like to suggest that we stop using this non-standard field, and > instead simply leave the FCS bytes on the end of frames that go to > Radiotap interfaces. The presence of FCS bytes can be indicated in > the Radiotap header by setting the IEEE80211_RADIOTAP_F_FCS bit in > the IEEE80211_RADIOTAP_FLAGS field. This field is part of the standard. > > Any objections to this change? None from me. Just please make sure that it doesn't break tcpdump and wireshark. By the way, I'm thinking that maybe MadWifi should always use radiotap header in the monitor mode. If all userspace programs support it, there is no point in supporting other formats. Kernel modules should strive to be simple. -- Regards, Pavel Roskin |