title: icmp port unreachable error message
body: <p>I am sending UDP packets from one PC to another. I am watching the the whole activity using Wire Shark. I notice that for some time there is smooth transmission of packets from one system to the other. Then suddenly <code>ICMP</code> packets with error <code>'port unreachable'</code> starts to appear. Then they disappear for some time and there is again smooth transmission of UDP packets. Then these ICMP packets again appear with the same 'port unreachable' error. Then these ICMP packets disappear again and so on. And this continues in a periodic manner. </p>
  
  <p>Can anybody shed some light that what could be the reason for it.</p>
  
  <p><img src="https://i.stack.imgur.com/w2oy5.png"></p>