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Full Discussion: tcpdump filter (mis)behaviour
Operating Systems Linux Debian tcpdump filter (mis)behaviour Post 302505349 by Hollinch on Wednesday 16th of March 2011 06:33:14 PM
Old 03-16-2011
tcpdump filter (mis)behaviour
Hello, I am a bit puzzled. I am trying to capture data using tcpdump on a bonded interface, which works fine until I add a filter, then nothing is seen nor captured by libpcap/tcpump.

I have interfaces eth3 and eth4 bonded to bond0 because I am using a tap in a firewall connection to monitor all in and outgoing traffic.

All is fine if I just run tcpdump on the bond0 interface - all traffic is correctly shown. As soon as I specify a filter nothing seems to be seen nor captured anymore.

Some examples of command lines I tried:
Code:
/usr/local/sbin/tcpdump -i bond0 -nn tcp port 80
/usr/local/sbin/tcpdump -i bond0 -nn tcp port http



For example, without filters output is shown as here (and http traffic was seen to be present):

Code:
root@lins01:~# /usr/local/sbin/tcpdump -i bond0 -nn
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on bond0, link-type EN10MB (Ethernet), capture size 96 bytes
23:07:30.871053 IP 192.168.192.239.22 > 192.168.192.1.58229: Flags [P.], ack 2019718192, win 382, options [nop,nop,TS val 1091628665 ecr 724203], length 112
23:07:30.871291 IP 192.168.192.239.22 > 192.168.192.1.58229: Flags [P.], ack 1, win 382, options [nop,nop,TS val 1091628665 ecr 724203], length 112
23:07:30.871540 IP 192.168.192.239.22 > 192.168.192.1.58229: Flags [P.], ack 1, win 382, options [nop,nop,TS val 1091628665 ecr 724203], length 192
23:07:30.871553 IP 192.168.192.239.22 > 192.168.192.1.58229: Flags [P.], ack 1, win 382, options [nop,nop,TS val 1091628665 ecr 724203], length 192
23:07:30.892570 IP 192.168.192.1.58229 > 192.168.192.239.22: Flags [.], ack 112, win 6032, options [nop,nop,TS val 724205 ecr 1091628665], length 0
23:07:30.892773 IP 192.168.192.239.22 > 192.168.192.1.58229: Flags [P.], ack 1, win 382, options [nop,nop,TS val 1091628670 ecr 724205], length 384
23:07:30.892780 IP 192.168.192.239.22 > 192.168.192.1.58229: Flags [P.], ack 1, win 382, options [nop,nop,TS val 1091628670 ecr 724205], length 192

With a valid filter specified it sits forever, and finally when I terminate tcpdump it shows 0 packets captured, 0 packets received by filter and 0 packets dropped by kernel. As if no traffic of the specified nature was present, while I am certain it is.

The OS is Debian 5.0.8, with tcpdump version 3.9.8 and libpcap version 0.9.8. I also tried to upgrade to tcpdump 4.0.0 and libpcap 1.0.0, but the result is the same.

I tried to remove the bond and just monitor on one of the individual interfaces, but this still did not produce any results with filters specified (without filters I correctly see half of my traffic, send or receive, depending on which interface I select).

Anyone has any suggestions what to try to get filters working?

Many thanks in advance for your help.


 

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LEARN ABOUT DEBIAN

lire::firewall::ipfilterdlfconverter

IpfilterDlfConverter(3pm)				  LogReport's Lire Documentation				 IpfilterDlfConverter(3pm)

NAME

       Lire::Firewall::IpfilterDlfConverter - convert ipf (ipmon) logs to firewall DLF

DESCRIPTION

       Lire::Firewall::IpfilterDlfConverter converts Ipfilter logs into firewall DLF format.  Input for this converter is the standard ipf syslog
       log file as produced by ipmon. IP Filter is shipped with FreeBSD, OpenBSD (up to 2.9) and some other OS's.

EXAMPLE

       A ipfilter logfile which looks like

	Oct 30 07:42:29 rolle ipmon[16747]: 07:42:28.585962	ie0 @0:9
	 b 192.168.48.1,45085 -> 192.168.48.2,22 PR tcp len 20 64 -S OUT
	Oct 30 07:40:24 rolle ipmon[16747]: 07:40:23.631307	ep1 @0:6
	 b 192.168.26.5,113 -> 192.168.26.1,3717 PR tcp len 20 40 -AR OUT
	Oct 30 07:42:29 rolle ipmon[16747]: 07:42:28.585962	ie0 @0:9
	 b 192.168.48.1,45085 -> 192.168.48.2,22 PR tcp len 20 64 -S OUT
	Oct 30 07:44:11 rolle ipmon[16747]: 07:44:10.605416 2x	   ep1 @0:15
	 b 192.168.26.1,138 -> 192.168.26.255,138 PR udp len 20 257  IN
	Oct 30 07:44:34 rolle ipmon[16747]: 07:44:33.891869	ie0 @0:10
	 b 192.168.48.1,23406 -> 192.168.48.2,22 PR tcp len 20 64 -S OUT
	Oct 30 07:49:13 rolle ipmon[16747]: 07:49:12.554420	ep1 @0:15
	 b 210.132.100.117 -> 192.168.26.5 PR icmp len 20 56 icmp 3/3 for
	 192.168.26.5,61915 - 210.132.100.117,53 PR udp len 20 23040 IN
	Oct 30 07:50:23 rolle ipmon[16747]: 07:50:22.908107	ep1 @0:15
	 b 210.132.100.117 -> 192.168.26.5 PR icmp len 20 56 icmp 3/3 for
	 192.168.26.5,4480 - 210.132.100.117,53 PR udp len 20 19712 IN
	Oct 30 07:56:11 rolle ipmon[16747]: 07:56:11.113029 2x	   ep1 @0:15
	 b 192.168.26.1,138 -> 192.168.26.255,138 PR udp len 20 257  IN

       (that's: .... 'PR' protocol 'len' length_of_ip_headers_saved packetlength direction) will get converted to something like

	994398737 denied igmp 100.187.115.1 - ep1 LIRE_NOTAVAIL 
	 224.0.0.2 - 56
	994398861 denied igmp 100.187.115.1 - ep1 LIRE_NOTAVAIL 
	 224.0.0.1 - 56
	994398862 denied igmp 100.187.115.1 - ep1 LIRE_NOTAVAIL 
	 224.0.0.2 - 56
	994406849 denied udp 192.168.26.4 137 ie0 LIRE_NOTAVAIL 
	 192.168.26.255 137 116
	994406850 denied udp 192.168.26.4 137 ie0 LIRE_NOTAVAIL 
	 192.168.26.255 137 116
	994406866 denied udp 192.168.26.4 137 ie0 LIRE_NOTAVAIL 
	 192.168.26.255 137 98

SEE ALSO

       ipl(4) for description of log structure.

       The ipmon.c source (e.g. on

	http://www.openbsd.org/cgi-bin/cvsweb/~checkout~/ 
	 src/usr.sbin/ipmon/Attic/ipmon.c?rev=1.27& 
	 content-type=text/plain&hideattic=0

       ) for the specification of the log syntax.

       The IP Filter webpage on http://coombs.anu.edu.au/~avalon/ip-filter.html

AUTHOR

       Joost van Baal <joostvb@logreport.org>, Wessel Dankers <wsl@logreport.org>

VERSION

       $Id: IpfilterDlfConverter.pm,v 1.7 2009/03/15 08:10:55 vanbaal Exp $

COPYRIGHT

       Copyright (C) 2001-2003 Stichting LogReport Foundation LogReport@LogReport.org

       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
       MERCHANTABILITY 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 (see COPYING); if not, check with
       http://www.gnu.org/copyleft/gpl.html.

Lire 2.1.1							    2009-03-15						 IpfilterDlfConverter(3pm)
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