title: How and why do servers use random port numbers?
body: <p>Well-known services usually use a pre-defined port number on the server-side.</p>
  <p>However, I realized that that is not always the case. Some services and games for example seem to pick a random port from a pre-defined range.</p>
  <p>when you connect to a pre-defined port number, you send a request first, so the client's port can be determined, but if the service's port is not predetermined, how does the client know to which port to send the request? Also, what is the reason for always using a different port and how does this happen?</p>