title: Why UDP does not employ the path MTU?
body: <p>According to my knowledge, UDP does not use the path MTU to avoid fragmentation which however TCP does. I am trying to come up a reason to this particular design. </p>
  
  <p>TCP needs to avoid fragmentation because it has to retransmit the whole datagram even if just one fragment is dropped. On the contrary, UDP does not need to retransmit datagram, it's up to the application layer to ensure the integrity.</p>
  
  <p>In conclusion, fragment will slow the TCP transport protocol but not UDP transport protocol.</p>
  
  <p>Here comes the problem, for communication that need integrity, whether employ TCP which natrually guarantee the integrity, or develop an application layer retransmit protocol upon UDP, it will need to resend the whole datagram if not ACKed. Then, fragmentation will slow down application layer retransmit protocol upon UDP just the same as TCP. </p>
  
  <p>What's wrong with my reasoning?</p>