title: Directed UDP to IP address that doesn't exist
body: <p>I am experiencing slowdowns when attempting to send a UDP message to an IP address that is non-existent. We read a list of IP/ports out of a configuration file and expect that those combinations will exist. In some situations, the remote machine may not be online yet and the IP will not exist on the network. In this case, i would prefer that we do not attempt to send the data.</p>
  
  <p>I'm looking for suggestions on a good way to determine that the IP doesn't exist in order to skip sending the data. I do not want to completely remove it from the list because there is the chance that the machine may come online and i'd like to continue sending data.</p>
  
  <p>Relevant code:</p>
  
  <pre><code>int SendData(const char *data, int size, bool openIfClosed)
      {
          std::lock_guard&lt;std::mutex&gt; lock(sendMutex);        
  
          //if the socket was not already opened, close it after i do my send
          bool closeAfterSend = mySocket == INVALID_SOCKET ? true : false;
  
          if (!OpenSocket(openIfClosed))                              
              return 0;
  
          sockaddr_in address;
          address.sin_family = AF_INET;
          address.sin_port = htons(remotePort);
          address.sin_addr.s_addr = remoteIPAddress.GetIPAddressAsULong();             
  
          //check if remote address exists prior to send?
          int bytesSent = sendto(mySocket, data, 
                          size, 0, (struct sockaddr *)&amp;address, sizeof(address));
          if (bytesSent == size)
              numMsgsOut++;
          else
          {
             //fail
          }
  
  
          if (closeAfterSend &amp;&amp; openIfClosed)
          {
              closesocket(mySocket);
              mySocket = INVALID_SOCKET;
          }
  
          return bytesSent;
      }
  </code></pre>