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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
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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PACKET.PKT(1)							 packet.pkt 1.0.1						     PACKET.PKT(1)

NAME
packet.pkt - Pkt module DESCRIPTION
Provides the object for a packet and the string representation of the packet. This object has an attribute for each of the layers in the packet so each layer can be accessed directly instead of going through each layer. To access the nfs layer object you can use 'x.nfs' instead of using 'x.ethernet.ip.tcp.rpc.nfs' which would very cumbersome to use. Also, since NFS can be used with either TCP or UDP it would be harder to to access the nfs object independently or the protocol. Packet object attributes: Pkt( record = Record information (frame number, etc.) ethernet = ETHERNET II (RFC 894) object ip = IPv4 object tcp = TCP object rpc = RPC object nfs = NFS object ) CLASSES
class Pkt(baseobj.BaseObj) Packet object Usage: from packet.pkt import Pkt x = Pkt() Methods defined here: --------------------- __str__(self) String representation of object The representation depends on the verbose level set by debug_repr(). If set to 0 the generic object representation is returned. If set to 1 the representation of is condensed into a single line. It contains, the frame number, IP source and destination and/or the last layer: '1 0.386615 192.168.0.62 -> 192.168.0.17 TCP 2049 -> 708, seq: 3395733180, ack: 3294169773, ACK,SYN' '5 0.530957 00:0c:29:54:09:ef -> ff:ff:ff:ff:ff:ff, type: 0x806' '19 0.434370 192.168.0.17 -> 192.168.0.62 NFS v4 COMPOUND4 call SEQUENCE;PUTFH;GETATTR' If set to 2 the representation of the object is a line for each layer: 'Pkt( RECORD: frame 19 @ 0.434370 secs, 238 bytes on wire, 238 bytes captured ETHERNET: 00:0c:29:54:09:ef -> e4:ce:8f:58:9f:f4, type: 0x800(IPv4) IP: 192.168.0.17 -> 192.168.0.62, protocol: 6(TCP), len: 224 TCP: src port 708 -> dst port 2049, seq: 3294170673, ack: 3395734137, len: 172, flags: ACK,PSH RPC: CALL(0), program: 100003, version: 4, procedure: 1, xid: 0x1437d3d5 NFS: COMPOUND4args(tag='', minorversion=1, argarray=[nfs_argop4(argop=OP_SEQUENCE, ...), ...]) )' SEE ALSO
baseobj(1) BUGS
No known bugs. AUTHOR
Jorge Mora (mora@netapp.com) NFStest 1.0.2 10 April 2013 PACKET.PKT(1)
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