Re: capture certain bit in ICMP package

[Guy Harris <guy () alum mit edu>]

On Aug 21, 2011, at 12:40 PM, Martin T wrote:

> I would like to capture only the value of 108'th and 110'th bit in
> ICMP echo request packet. Those bits should reside in ICMP payload
> area. Is there a possibility in tcpdump to capture only specific bit?

What do you mean by "capture only specific bit[s]"?  There is no mechanism that would cause only those bits to be saved 
in a capture file.

> Or at least show the "tcpdump -i eth0 -n -X" output in binary instead
> of hexadecimal?

"-X" should continue to be hex.  An option could be added to print in binary, but it'd probably be somewhat rarely 
used; the quickest solution might be to pipe the output of tcpdump to a script that translates hex to binary.

What is it you're *really* trying to do here?  You could perhaps use a capture filter to capture only packets that have 
particular values in those bits.-
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