title: getting page cannot be displayed IIS
body: <p>One of my users reported that they got an error page saying "Page cannot be displayed" when they try to post a page (submit button), but when they resubmit the page (refresh) the request sent successfully to the server. This error appears randomly some of the request sent successfully from the first time but a little of them causes this issue. </p>
  
  <p>I have checked the below:</p>
  
  <ul>
  <li>no application errors</li>
  <li>increase the max requestlength, session timeout, </li>
  <li>the issue appears only for remote users (different network)</li>
  <li>I checked IIS log and found some requests with both status 400 and 500 with win-status 64, which means there was a network issue when the server responses to the request (as I understand this code, failed to receive an acknowledgment from the client, please confirm)</li>
  <li>the URL is added to the proxy exceptions on the client side, so there is no proxy</li>
  <li>the server is not loaded, server performance is excellent</li>
  <li>the issue appears after clicking submit button immediately, so we don't think it's related to a timeout issue between the server and client or between the server and database server. and after refresh, it submitted successfully with no delays</li>
  <li>we removed all servers except one from the load balancer to eliminate any issue related to load balancing</li>
  <li>SSL certificate is verified and checked</li>
  <li>we moved some internal users to user the "external application firewall" (where the issue appears) and they did not report any issue</li>
  </ul>
  
  <p>Now, a brief description of the environment setup:</p>
  
  <ul>
  <li>the application server is a virtual server (VMware)</li>
  <li>the application firewall is F5 Firewall</li>
  <li>SSL certificate installed on application firewall to encrypt and decrypt the requests</li>
  </ul>
  
  <p>A final note: we ran wireshark on the server and we have noticed that there are a lot of dropped packets on requests and "disordered packets", we increased the buffer size for the network driver, but still there are dropped packets appear on wireshark</p>
  
  <p>Below is a map for sending request from client to server:</p>
  
  <p>Client network -http<strong>s</strong>-> private network -http<strong>s</strong>-> Firewall -http<strong>s</strong>->application Firewall -http-> load balancer -http-> Application server --> database server.</p>
  
  <p>Do you have any suggestions on how to resolve this issue or what is the issue exactly?</p>
  
  <p>UPDATE: i checked network and noticed that request is aborted as screenshot below,<a href="https://i.stack.imgur.com/5hfJp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5hfJp.png" alt="enter image description here"></a></p>
  
  <p>and on fiddler i got this message as response (i don't know if its related to fiddler or is the actual response:</p>
  
  <blockquote>
    <p>SendRequest() failed: System.IO.IOException Unable to write data to
    the transport connection: An existing connection was forcibly closed
    by the remote host. &lt; An existing connection was forcibly closed by
    the remote host</p>
  </blockquote>