title: Strange UDP issue on Windows 10
body: <p>I'm experiencing a very strange issue on Windows 10. Sending from one UDP socket to another, both on the same local network interface, doesn't work.</p>
  
  <ul>
  <li>Sending to the same UDP socket works as expected</li>
  <li>Sending to/from another machine works as expected</li>
  <li>If I'm using the loopback interface (127.0.0.1), it works as expected</li>
  <li>I tried several interfaces (sending from an interface to itself), and even different addresses on the same interface - nothing seems to work.</li>
  <li>This works as expected on Windows 7 and on Linux.</li>
  <li>Port binding succeeds.</li>
  </ul>
  
  <p>It worked fine until a few days ago, and I have no idea what broke it.</p>
  
  <p>The following ruby script demonstrates the problem:</p>
  
  <pre><code>#!/usr/bin/env ruby
  
  require 'socket'
  
  addr = IPSocket.getaddress(Socket.gethostname)
  u1 = UDPSocket.new
  u1.bind(addr, 5010)
  u2 = UDPSocket.new
  u2.bind(addr, 5020)
  u1.send('abcd', 0, addr, 5010)
  p u1.recvfrom(4) # Works
  u1.send('abcd', 0, addr, 5020)
  p u2.recvfrom(4) # Fails
  </code></pre>