title: connected udp multicast needs bind in the sender side
body: <p>I have an ambiguous issue, I have a multicast group between two users one of them is a sender and another is receiver I did these scenarios in each side:</p>
  
  <p>Receiver:</p>
  
  <ol>
  <li>create a udp socket.</li>
  <li>bind to a multicast group address</li>
  <li>connect to the sender side ( connect(sender ip))</li>
  <li>join the multicast group </li>
  <li>recv from the multicast group.</li>
  </ol>
  
  <p>Sender:</p>
  
  <ol>
  <li>create a udp socket.</li>
  <li>send to the multicast group.</li>
  </ol>
  
  <p>In this scenario above when sender sent data receiver couldn't receive but if we checked the receiver side by tcpdump there is data was received from multicast group.
  but if there is no connect to sender side in receiver, data will be received.</p>
  
  <p>BUT Actually, If we let the sender bind to the multicast address before send to the multicast group and also receiver connect to the sender side as scenario above data will be received successfully!!!!
  Any explanation when we added the bind in the sender side ??? </p>