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Operating Systems Linux Debian tcpdump filter (mis)behaviour Post 302506591 by Hollinch on Monday 21st of March 2011 09:56:44 AM
Old 03-21-2011
OK I found it, with Google's help...

Apparently I need to add 'vlan and ...' to my filter expression when VLANs are used. Without filter expression, tcpdump and libpcap just output everything, but as soon as filters are specified, the vlan tagging needs to be specified.

See here Blog Stéphane Bortzmeyer: Un exemple de panne amusante de tcpdump

Hope it is useful to others as well.
 

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DRIFTNET(1)						      General Commands Manual						       DRIFTNET(1)

NAME
driftnet - capture images from network traffic and display them in an X window; optionally, capture audio streams and play them. SYNOPSIS
driftnet [options] [filter code] DESCRIPTION
Driftnet watches network traffic, and picks out and displays JPEG and GIF images for display. It is an horrific invasion of privacy and shouldn't be used by anyone anywhere. It has been described as `a graphical tcpdump(8)', `EtherPeg for Unix', and called all sorts of nasty names by people on Freshmeat. It is also possible to use driftnet to capture MPEG audio data from the network and play it through a player such as mpg123(1). Images may be saved by clicking on them. OPTIONS
-h Print a summary of usage. -v Print additional details of packets captured to the terminal. -b Beep when a new image is displayed. -i interface Listen to packets on interface. By default, driftnet will try to pick up traffic on all interfaces, but this does not work with all versions of pcap(3); on such systems, an interface must be specified. On some systems, driftnet can only use promiscuous mode if an interface is specified. -f file Instead of listening on an interface, read captured packets from a pcap(3); dump file; file can be a named pipe for use with Kismet or similar. -p Do not put the interface into promiscuous mode. -a Operate in `adjunct mode', where driftnet gathers images for use by another program, such as Jamie Zawinski's webcollage. In this mode, no window is displayed; images are captured and saved in a temporary directory, and their names written on standard output. -m number In adjunct mode, silently drop images if there are more than number in the temporary directory. It is assumed that another process will delete images which it has processed. -x prefix The filename prefix to use when saving images, by default `driftnet-'. -d directory Use directory to store temporary files. Driftnet will clear this directory of its own temporary files on exit, but will not delete the directory or any other files. -s Attempt to capture streamed audio data from the network, and either play it or, in adjunct mode, save it in files. At present this only works with MPEG data. -S Capture streamed audio data only, ignoring images. -M command Use the named command to play MPEG audio data. The command, which is executed using the shell, should accept MPEG frames on standard input. The default is `mpg123 -'. filter code Additional filter code to restrict the packets captured, in the libpcap syntax. User filter code is evaluated as `tcp and (filter code)'. SEE ALSO
tcpdump(8), pcap(3), webcollage(1), mpg123(1), http://www.etherpeg.org/, http://freshmeat.net/projects/driftnet/, http://www.ex-parrot.com/~chris/driftnet/. AUTHOR
Chris Lightfoot <chris@ex-parrot.com> VERSION
Driftnet, version 0.1.6. $Id: driftnet.1.in,v 1.7 2004/04/26 14:42:36 chris Exp $ COPYING
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MER- CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. DRIFTNET(1)
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