title: Why TCP not recved ACK from server in Solaris machine?
body: <p>In the client side , sftp application send some packet to ssh server port 22.</p>
  
  <p>SFTP application send packet to TCP , from etherial capture we can see that 
  sftp packet send from application to TCP and TCP send to packet to server but TCP not recieved TCP ACK from the server so TCP again send the packet after few second but still no response from server..</p>
  
  <p>It  seems that server no received the packet from client.</p>
  
  <p>Client SFTP allication wait in select for TCP recv with timeout of 120 second
  after 120 second application get timeout from select and close the SFTP operation 
  with timeout error.</p>
  
  <p>In capture I can see TCP retransmit packet many times but fail to recv server TCP ACK.</p>
  
  <p>Scenario:
  1. Timeout happen sometime only.
  2. After this issue next SFTP opration[upload] success with same server.
  3. It seems network has no issue because next upload is working fine.
  4. both client and server has SOLARIS OS
  5. we are unable to reproduce this in our Lab environment
  6. This issue happen only in real customer network.
  7. Appln is in C language. SSH server is Open SSH server.</p>
  
  <p>I want to know:
  1. How can we found reason for  TCP not recv ACK repply form Server.
  2. Is any TCP system setting in solaris cause this issue.
  3. please provide any inforamtion so that we can resolve this issue.</p>