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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aggregate-ios

AGGREGATE-IOS(1)					      General Commands Manual						  AGGREGATE-IOS(1)

NAME

       aggregate-ios - optimise a concatenated set of cisco/IOS prefix filters to help make them nice and short.

SYNOPSIS

       aggregate-ios <source_config >optimised_config

DESCRIPTION

       Takes  cisco IOS configuration on stdin, and optimises any prefix filters found using aggregate(1).  Optimised filters are produced on std-
       out.

OPTIONS

       None.

DIAGNOSTICS

       Any diagnostics produced by aggregate(1) are passed through on stderr.

EXAMPLES

       The following configuration fragment:

	 ip prefix-list AS65530 description Foo, Inc
	 ip prefix-list AS65530 permit 10.1.0.0/16
	 ip prefix-list AS65530 permit 10.2.0.0/16
	 ip prefix-list AS65530 permit 10.2.1.0/24
	 ip prefix-list AS65530 permit 10.3.0.0/16
	 ip prefix-list AS65531 description Bar.Com
	 ip prefix-list AS65531 seq 5 permit 192.168.1.0/24
	 ip prefix-list AS65531 seq 10 permit 192.168.2.0/24
	 ip prefix-list AS65531 seq 15 permit 192.168.0.0/19

       is optimised as follows:

	 ip prefix-list AS65530 permit 10.1.0.0/16 le 24
	 ip prefix-list AS65530 permit 10.2.0.0/15 le 24
	 ip prefix-list AS65531 permit 192.168.0.0/19 le 24

SEE ALSO

       aggregate(1)

HISTORY

       Aggregate-ios was written by Joe Abley <jabley@mfnx.net>.

BUGS

       All those in aggregate(1) and then some :)

Joe Abley							 2000 November 27						  AGGREGATE-IOS(1)