title: "Can't assign requested address" when sending to a UdpSocket
body: <pre><code>let addr = "239.255.255.250:1982";
  let socket = UdpSocket::bind(addr).unwrap();
  let message = "some message".as_bytes();
  socket.send_to(message, addr).unwrap();
  </code></pre>
  
  <p>This code gives the following error for the last line:</p>
  
  <pre class="lang-none prettyprint-override"><code>Error { repr: Os { code: 49, message: "Can\'t assign requested address" } }
  </code></pre>
  
  <p>Why would that be the case?</p>
  
  <p>EDIT:
  I tried the following as suggested:</p>
  
  <pre><code>let addr = "239.255.255.250:1982";
  let socket = UdpSocket::bind("127.0.0.1:34254").unwrap();
  let message = "some message".as_bytes();
  socket.send_to(message, addr).unwrap();
  </code></pre>
  
  <p>But that didn't change anything, unfortunately.</p>