tcpdump filter (mis)behaviour Post: 302505349

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Operating Systems Linux Debian tcpdump filter (mis)behaviour Post 302505349 by Hollinch on Wednesday 16th of March 2011 06:33:14 PM

03-16-2011

Registered User

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.

Hollinch

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tgt-setup-lun

tgt-setup-lun(8)					      System Manager's Manual						  tgt-setup-lun(8)

NAME

       tgt-setup-lun - creates a target, adds a device to the target and defines initiators that can connect to the target

SYNOPSIS

       tgt-setup-lun -d device -n target_name [initiator_IP1 initiator_IP2 ...] [-h]

DESCRIPTION

       Starts tgtd if necessary and creates a target according to the supplied target_name. The format of the target name is as follows:
       iqn.2001-04.com.<hostname>-<target_name> The target name must be unique.

       The  script then adds the requested device to the target. If specific IP addresses are defined, it adds them to the list of allowed initia-
       tors for that target. If no IP addresses is defined, it defines that the target accepts any initiator.

EXAMPLES

       Create a target that uses /dev/sdb1 and allows connections only from 192.168.10.81:
       tgt-setup-lun -d /dev/sdb1 -n my_target 192.168.10.81

       Create a target that uses /dev/sdb1 and allows connections only from 192.168.10.81 and 192.168.10.82:
       tgt-setup-lun -d /dev/sdb1 -n my_target 192.168.10.81 192.168.10.82

       Create a target that uses /dev/sdb1 and allows connections from any initiator:
       tgt-setup-lun -d /dev/sdb1 -n my_target

       Display help:
       tgt-setup-lun -h

AUTHOR

       Written by Erez Zilber

REPORTING BUGS

       Report bugs to <erezz@voltaire.com>.

COPYRIGHT

       Copyright (C) Voltaire Ltd. 2008.

																  tgt-setup-lun(8)