title: UDP packets are dropped when its size is less than 12 byte in a certain PC. how do i figure it out the reason?
body: <p>i've stuck in a problem that is never heard about before.</p>
  
  <p>i'm making an online game which uses UDP packets in a certain character action. after i developed the udp module, it seems to work fine. though most of our team members have no problem, but a man, who is my boss, told me something is wrong for that module.</p>
  
  <p>i have investigated the problem, and finally i found the fact that... on his PC, if udp packet size is less than 12, the packet is never have been delivered to the other host.</p>
  
  <p>the following is some additional information:</p>
  
  <ul>
  <li>1~11 bytes udp packets are dropped, 12 bytes and over 12 bytes packets are OK.</li>
  <li>O/S: Microsoft Windows Vista Business</li>
  <li>NIC: Attansic L1 Gigabit Ethernet 10/100/1000Base-T Controller</li>
  <li>WSASendTo returns TRUE.</li>
  <li>loopback udp packet works fine.</li>
  </ul>
  
  <p>how do you think of this problem? and what do you think... what causes this problem?
  what should i do for the next step for the cause?</p>
  
  <p>PS. i don't want to padding which makes length of all the packets up to 12 bytes.</p>