Applies To:
  • CitectSCADA 6.XX
  • CitectHMI 6.XX

My IO server is taking a long time to startup after changing from windows 2000 to Windows XP. I have tried tuning the IO Driver and IO server parameters and found that it makes little difference.

Check the event view for message Event ID 4226 (Event Viewer, under System - look for TCP/IP Warnings saying: "TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts) message.  If found, the problem is due to windows limiting the number of incomplete socket connections made from a single system that can be created. This is a capped at to 10 per second.

This problem seems to manifest itself where there are a large amount of connections on a system (i.e. 20 or more IO devices using TCPIP for a transport protocol). Once all connections are made then it should be possible for your system to perform at a normal level as the problem only affect incomplete connections.

The reason for this limitation is to reduce the risk of an attack by worms and spamers by reducing the amount of random connection that a single computer can attempt to open. A patch is available from the web site, it should be noted that this is not supported by Citect and Microsoft as it involves making a change to one of the core networking files. The problem does not effect the Windows 2003 server or windows XP sp1.

IO Server Slow, Widows XP, TCPIP, Ethernet, Connections