title: netcat: listen and capture TCP packets
body: <p>Is it possible to just listen(not create a new connection) for TCP packets on a port which is already in use, i.e. is sending over data from a router to a server.</p>
  
  <p>I am aware that the following starts the listening process on the mentioned port, and saves it in the <code>pcap</code> file:</p>
  
  <p>SERVER SIDE: <code>nc  -l -p &lt;port&gt; &gt; file_name.pcap</code></p>
  
  <p>CLIENT SIDE: <code>sudo tcpdump -s 0 -U -n -i eth0 not host &lt;server_ip&gt; -w file_name.pcap | nc &lt;server_ip&gt; &lt;port&gt;</code></p>
  
  <p>But this creates a new connection on the given port and captures packet related to it. I want to capture packets on a port which is already being used to send packets.</p>