title: Where is the Don't Fragment Bit of the IP Flags used?
body: <p>I am curious to know where the "Don't Fragment" [DF] Bit of the IP Flags is used. As fragmentation is invisible to higher layers and they don't care too.</p>
  
  <p>I am also looking for an example. </p>
  
  <p>Thanks a lot in advance.</p>