title: UDP: How does the client know its server?
body: <p>I'm sniffing between two devices which communicate in a duplex fashion via udp. I'm using wireshark to sniff. The config file for the first device (a piece of hardware under test) states that the client port is 54718 and the server is 54717. In the config file for the second device (a simulator written years ago), only one port is specified. That of 54718. </p>
  
  <p>The two devices communicate without any problems.</p>
  
  <p>But how does the second device manage to connect and send to 54717 when it has no knowledge of it? </p>
  
  <p>In wireshark I can see that the first device is sending to the second device such that the source port is 54717 and the destination is 54718. I can also see that the second device is sending to the first device such that the source port is 54718 and the destination is 54717.</p>
  
  <p>The first device sends first and the protocol is described as that of UDP in Wireshark. The simulator replies, also via UDP. Subsequent exchanges are described as being STUN ChannelData TURN Messages. I've no knowledge of this protocol but maybe it explains why I don't see 54717 in the simulators config file.</p>
  
  <p>Thanks for your help,</p>
  
  <p>Barry</p>