The "Open Connections" value does not decrease when half-open CIFS connections (no SYN ACK) have occurred.

No SYN ACK traffic is below image.
PC           SG          OCS
----------------> SYN(139 and 445)
            -------> SYN(139 and 445)
<--------X------- no SYN ACK

The value decreased when the ProxySG was restarted. I created 10000 half -open CIFS connections (no SYN ACK). However, the value did not exceed 2000.

Does ProxySG have a limit on the number of half-open connections?
 

This limit is by design. These connections are shown on the Errored Sessions report.  The ProxySG keeps these sessions on the list as a way to allow proxy admins to investigate issues for a period of time after the issue occurs. The ProxySG has to limit the number of sessions so that keeping track of all these sessions doesn't consume all the memory on the appliance.

Here are the limits by model.

Model    Limit
--------------------
SG9000   2000
SG300    2000
SG810    2000
SG510    1000
SG210    1000