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06-15-2012, 11:00 AM
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#1
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LQ Newbie
Registered: Jun 2012
Posts: 3
Rep: 
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capturing packets with tcpdump
Hello
I have a lot of processes in the network between network elements.
I want to capture some HTTP/SOAP packets which contain specific value. This packet can arrive at any time so it's not possible to capture all the traffic as there is a lot of it.
Is it possible to set some filter to capture only those packets?
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06-15-2012, 12:17 PM
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#2
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Moderator
Registered: May 2001
Posts: 29,415
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Yes, it's possible.
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06-15-2012, 12:37 PM
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#3
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LQ Newbie
Registered: Jun 2012
Posts: 3
Original Poster
Rep:
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How?
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06-15-2012, 12:49 PM
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#4
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Moderator
Registered: May 2001
Posts: 29,415
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A BPF filter can help with protocol (TCP) port (80) and packet headers like SYN, narrowing down the amount of traffic you log with tcpdump, tshark or whatever you use. And although the application interprets the payload as XML SOAP IIRC is just plain text you can grep.
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06-15-2012, 01:55 PM
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#5
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LQ Newbie
Registered: Jun 2012
Posts: 3
Original Poster
Rep:
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so if i'll execute
tcpdump -s0 -w file.cap -i eth0 |grep 42507
will work?
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06-15-2012, 04:18 PM
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#6
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Moderator
Registered: May 2001
Posts: 29,415
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Yeah, it'll work.
But what the result is remains to be seen using grep in that way.
Better save the capture though and use Wireshark as it has a lot of dissectors.
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