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POCapture server-client communication with tcpdump
 

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    <p>I wrote a simple server and client apps, where I can switch between TCP, DCCP and UDP protocols. The goal was to transfer a file from the one to the other and measure the traffic for each protocol, so I can compare them for different network setups (I know roughly what the result should be, but I need exact numbers/graphs). Anyway after starting both apps on different computers and starting tcpdump I only get in the tcpdump-log the first few MBs (~50MB) from my 4GB file. The apps are written in a standard C/C++ code, which could be found anywhere on the web. What may be the problem or what could I be doing wrong here? </p> <p>-- <em>Edit</em></p> <p>The command line I use is:</p> <pre><code>tcpdump -s 1500 -w mylog </code></pre> <p><strong>tcpdump</strong> captures then packets <strong>only the first ~55 sec</strong>. That's the time the client needs to send the file to the socket. Afterwards it stops, even though the server continues receiving and writing the file to the hard drive. </p> <p>-- <em>Edit2</em></p> <p><em>Source code</em>:</p> <p><a href="http://pastie.org/1066833" rel="nofollow noreferrer">client.cpp</a><br/> <a href="http://pastie.org/1066837" rel="nofollow noreferrer">server.cpp</a><br/> <a href="http://pastie.org/1066840" rel="nofollow noreferrer">common.hpp</a><br/> <a href="http://pastie.org/1066843" rel="nofollow noreferrer">common.cpp</a></p> <p>-- <em>Edit final</em></p> <p>As many of you pointed out (and as I suspected) there were several misconceptions/bugs in the source code. After I cleaned it up (or almost rewrote it), it works as needed with tcpdump. I will accept the <strong>answer from @Laurent Parenteau</strong> but only for <strong>point 5.</strong> as it was the only relevant for the problem. If someone is interested in the correct code, here it is:</p> <p><em>Source code edited</em></p> <p><a href="http://pastie.org/1090272" rel="nofollow noreferrer">client.cpp</a><br/> <a href="http://pastie.org/1090273" rel="nofollow noreferrer">server.cpp</a><br/> <a href="http://pastie.org/1090274" rel="nofollow noreferrer">common.hpp</a><br/> <a href="http://pastie.org/1090275" rel="nofollow noreferrer">common.cpp</a></p>
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    1. COby default tcpdump only captures the first handful of bytes in each packet. Did you tell it to capture everything, using the `-s snaplen` parameter ?
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    2. CO@nos, thanks! I tried it out, but still no luck. See my edit.
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    3. COCan you post the tcpdump command used to capture the network traffic?
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      1. USLaurent Parenteau
 

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