title: How to detect CDP by tcpdump
body: <p>I would like to ask you for help: Does somebody know how to detect Cisco Discovery Protocol via tcpdump?</p>
  
  <p>Currently I'm using following command, but I'm not sure by this:</p>
  
  <pre><code>tcpdump -i eth0 -nn "ether[20:2]==0x2000"
  </code></pre>
  
  <p>Some hints are appreciated. Thank you ...</p>
  
  <p>Charkh</p>