title: HTTP request does not reach the server occasionally. Why?
body: <p>We host our web-service on a dedicated server.
  Sometimes (I'd say 1 out of 20) a response is not received from the server.
  That makes the browser fallback with time-out error.</p>
  
  <p>An important detail: the request is not logged by Apache in this case.</p>
  
  <p>There is no load on Apache, there are a lot of free memory and CPU power left.</p>
  
  <p>[UPDATE]
  I have profiled the problem case with tcpdump utility.
  These are the good and bad sessions traced by tcpdump.
  The request is the same in both experiments.
  Good - server returns response.
  Bad - no response, time-out error.</p>
  
  <p>Do you see why the problem happens from these data?
  How can I move further to get closer to the source of the error?</p>
  
  <p>I've replaced my real ip address with 123.45.67.890</p>
  
  <pre><code>---- Bad ----
  12:23:36.366292 IP 123.45.67.890.61749 &gt; myserver.superbservers.com.www: S 2125316338:2125316338(0) win 8192 &lt;mss 1460,nop,wscale 2,nop,nop,sackOK&gt;
  12:23:39.362394 IP 123.45.67.890.61749 &gt; myserver.superbservers.com.www: S 2125316338:2125316338(0) win 8192 &lt;mss 1460,nop,wscale 2,nop,nop,sackOK&gt;
  12:23:45.365567 IP 123.45.67.890.61749 &gt; myserver.superbservers.com.www: S 2125316338:2125316338(0) win 8192 &lt;mss 1460,nop,nop,sackOK&gt;
  --------
  
  ---- Good ----
  12:27:07.632229 IP 123.45.67.890.63914 &gt; myserver.superbservers.com.www: S 3581365570:3581365570(0) win 8192 &lt;mss 1460,nop,wscale 2,nop,nop,sackOK&gt;
  12:27:10.620946 IP 123.45.67.890.63914 &gt; myserver.superbservers.com.www: S 3581365570:3581365570(0) win 8192 &lt;mss 1460,nop,wscale 2,nop,nop,sackOK&gt;
  12:27:10.620969 IP myserver.superbservers.com.www &gt; 123.45.67.890.63914: S 2654770980:2654770980(0) ack 3581365571 win 5840 &lt;mss 1460,nop,nop,sackOK,nop,wscale 6&gt;
  12:27:10.838747 IP 123.45.67.890.63914 &gt; myserver.superbservers.com.www: . ack 1 win 4380
  12:27:10.957143 IP 123.45.67.890.63914 &gt; myserver.superbservers.com.www: P 1:213(212) ack 1 win 4380
  12:27:10.957152 IP myserver.superbservers.com.www &gt; 123.45.67.890.63914: . ack 213 win 108
  12:27:10.965543 IP myserver.superbservers.com.www &gt; 123.45.67.890.63914: P 1:630(629) ack 213 win 108
  12:27:10.965621 IP myserver.superbservers.com.www &gt; 123.45.67.890.63914: F 630:630(0) ack 213 win 108
  12:27:11.183540 IP 123.45.67.890.63914 &gt; myserver.superbservers.com.www: . ack 631 win 4222
  12:27:11.185657 IP 123.45.67.890.63914 &gt; myserver.superbservers.com.www: F 213:213(0) ack 631 win 4222
  12:27:11.185663 IP myserver.superbservers.com.www &gt; 123.45.67.890.63914: . ack 214 win 108
  --------
  </code></pre>
  
  <p>Hosting: SuperbHosting
  OS: Ubuntu</p>