title: Windows 10 - SYN/ACK packet not sent in response to SYN packets
body: <p>I tried to run a simple 1-page site with Flask in Python on port 5000 of my computer <code>192.168.0.113</code>, which is running Windows 10. On the same computer, I can view the site by using <code>localhost:5000</code> in a web browser.</p>
  
  <p>I tried to use another computer <code>192.168.0.134</code> on the same LAN to view the site. However, <code>192.168.0.113</code> never replied with a <code>SYN/ACK</code> packet to the <code>SYN</code> packet from <code>192.168.0.134</code>, even if the firewall of <code>192.168.0.113</code> is completely turned off. This image is the captured flow of the packets:</p>
  
  <p><a href="https://i.stack.imgur.com/kuFBb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kuFBb.png" alt="image"></a></p>
  
  <p>If I did it reversely (i.e. <code>192.168.0.134</code> as the server to host the site, and <code>192.168.0.113</code> tried to connect as the client), then <code>192.168.0.113</code> is able to connect.</p>
  
  <p>I noted from some previous posts (especially <a href="https://serverfault.com/questions/235965/why-would-a-server-not-send-a-syn-ack-packet-in-response-to-a-syn-packet">this one</a>) that the problem can be solved by disabling TCP window scaling and TCP timestamps. I checked in <code>netsh</code> of <code>192.168.0.113</code> and noted that TCP window scaling had already been <code>disabled</code> and TCP timestamps was <code>normal</code>. I tried to disable both of them, and also tried to disable just one of them. However, all combinations failed and <code>192.168.0.113</code> still wonn't sent <code>SYN/ACK</code> packets in response to <code>SYN</code> packets from <code>192.168.0.134</code>.</p>
  
  <p>How can I get this fixed?</p>