title: Reply with unsupported protocol when writing custom network stack
body: <p>I have been writing my own version of the 802.11 protocol with network stack. This is mostly a learning experience to see more in depth on how networks work. </p>
  
  <p>My question is, is there a standard for replying to client devices that a certain protocol is unsupported?</p>
  
  <p>I have an android device connecting to my custom wifi device and immediately sending a TON of requests at the DNS port of my UDP protocol. Since I would like to test out other protocols I would very much like a way for my wifi device to tell the android device that DNS is not available and get it to quite down a little.  </p>
  
  <p>Thanks in advance!</p>