title: Understanding [TCP ACKed unseen segment] [TCP Previous segment not captured]
body: <p>We are doing some load testing on our servers and I'm using tshark to capture some data to a pcap file then using the wireshark GUI to see what errors or warnings are showing up by going to Analyze -> expert Info with my pcap loaded in..</p>
  
  <p>I'm seeing various things that I'm not sure or do not completely understand yet.. </p>
  
  <p>Under Warnings I have:
  779 Warnings for TCP:  ACKed segment that wasn't captured (common at capture start)
  446 TCP:  Previous segment not captured (common at capture start)</p>
  
  <p>An example is :
  40292   0.000   xxx xxx TCP 90  [TCP ACKed unseen segment] [TCP Previous segment not captured] 11210 > 37586 [PSH, ACK] Seq=3812 Ack=28611 Win=768 Len=24 TSval=199317872 TSecr=4506547</p>
  
  <p>We also ran the pcap file though a nice command that creates a command line column of data</p>
  
  <p>command</p>
  
  <pre><code>tshark -i 1 -w file.pcap -c 500000
  </code></pre>
  
  <p>basically just saw a few things in the tcp.analysis.lost_segment column but not many..\</p>
  
  <p>Anyone enlighten what might be going on? tshark not able to keep up with writing data, some other issue? False positive?</p>