Re: capturing on both interfaces simultaneously

[abhinav narain <abhinavnarain10 () gmail com>]

On Sun, Dec 11, 2011 at 9:04 PM, Gianluca Varenni <
Gianluca.Varenni () riverbed com> wrote:

> When you talk about 15% RAM, do you actually mean working set or virtual
> address space? Which version of linux are you using?
>
> I am using Openwrt on a Netgear router. Kernel 2.6.39
I see this usage by top command.
VSZ reports 9304 Bytes.I think this must be virtual address space.
I am not sure how to find the exact memory used by my code and by pcap/libz
library i am using.

Regarding 802.11a/b/g/n, you cannot rely much on the radiotap header of a
> beacon frame. The radiotap header will only tell you which band was the
> packet transmitted on (so "a" frequencies or "b/g" frequencies). In 99.9%
> of the cases, beacons are transmitted at the lowest rate possible in that
> specific band, so 1Mbps for "b/g" band and 6Mbps for the "a" band. You need
> to parse the beacon packet and understand which speeds are supported by the
> AP to distinguish between a,b,g and n.

Ok. The point is I can know only the fact that an AP is a supporting n or
not, at maximum ?
The rates showed in tcpdump can give me an indication of the AP is n
enabled or not ?
I am looking for alternative seeing into management frame and finding HT
Capability...

TCPdump code reads the radiotap header and classifies the channel
information using the radiotap header into the following :
fhss A,G (half/full duplex) , B,T , HT40+,HT40-
I am listening only for beacons in then network. Hence I notice I never see
anything apart from A, G. When is HT40+,40- transmitted in radiotap header
? in data frames ?

Will I ever see HT40+,40- in case of beacons.
Does this field in radiotap header (if it occurs) mean the interface beacon
came from was having the above (equivilantly n ) support ?
HT40+,- is essentially  n ?
So, do I need to look at any other type of frames than beacons... Or just
once AP support

On the "n" topic, remember that 802.11n can work on both the "a" band and
> the "b/g" band. It's just a new set of modulations that can be used for
> both bands.

Ok. So, there is nothing as a N beacon..
Only advertisements at 1,6 rate and then actual data at N speed.
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