From: Michael Wu <flamingice@sourmilk.net>
To: Andy Green <andy@warmcat.com>
Subject: Re: Question about PRISM2 header rate field
Date: Sun, 4 Mar 2007 22:10:48 -0500
Cc: Johannes Berg <johannes@sipsolutions.net>,
	linux-wireless@vger.kernel.org
References: <45EA9E39.6080706@warmcat.com> <1173053744.6131.40.camel@johannes.berg> <45EB6C3B.2060408@warmcat.com>
In-Reply-To: <45EB6C3B.2060408@warmcat.com>
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On Sunday 04 March 2007 20:02, Andy Green wrote:
> How about for injection on the Management interface, it expects to find
> a PRISM2 header prepended to the ieee80211 one and the payload, in
> exactly the same format as is delivered by Monitor Mode?  The PRISM2
> capture header structure has a bunch of fields for things like rate and
> antenna selection already.  This has the satisfying aspect that you can
> literally replay the whole Monitor Mode packet capture down the
> Management Interface and get it to go out at the same rate.
>
Isn't this what aircrack does? I think many other drivers that support fram=
e=20
injection do it in a similar way (TX AVS frame on monitor interface), and=20
this is also the way I prefer the frame injection interface. It does have t=
he=20
nice property of being able to directly replay captured traffic as you=20
mentioned. Just note that AVS/prism2 is planned to be removed in favor of=20
radiotap which is more extensible. Radiotap should also work for frame=20
injection, though it isn't as easy as using a fixed length header format.

Note that modifying the management interface to do this is possible, but it=
=20
would break hostap (and probably wpa_supplicant w/ MLME). Doing packet=20
injection on monitor interfaces instead is safer in that regard.

=2DMichael Wu

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