Cannot Reconnect to TN3270 Server with Close Listen Sockets

Last reviewed: December 31, 1997
Article ID: Q166846

The information in this article applies to:

Microsoft Windows NT Server versions 3.51 and 4.0
Microsoft SNA Server for Windows NT, versions 2.11 SP1, SP2 and 3.0

SYMPTOMS

When you configure the Microsoft SNA Server 2.11 or SNA Server 3.0 TN3270 Server to use the Close Listen Socket option, TN3270 clients are unable to reconnect to the TN3270 server even though LUA sessions are available.

When the Close Listen Socket option is enabled, the TN3270 service performs a CloseSocket() call when all SNA sessions are in use. The TN3270 service indicates this by logging the following Windows NT event:

   Event ID: 207
   Source: TN3270 Server
   Description:
   The TN3270E Server has closed the socket which listens for clients

While existing TN3270 client sessions continue to work normally, new TN3270 client connection requests are rejected immediately with a TCP/IP Reset. This allows the TN3270 client emulator to be notified of a connection failure so it can try a different TN3270 service for a session.

When a TN3270 client disconnects causing an SNA session to become available, the TN3270 service reopens the listen socket again and logs the following event:

   Event ID: 206
   Source: TN3270 Server
   Description:
   The TN3270E Server has opened a socket to listen for clients

However, TN3270 clients are still unable to reconnect until the TN3270 server is stopped and restarted or if all users disconnect from the TN3270 server.

CAUSE

When the TN3270 server calls the CloseSocket() function, the Windows NT TCP/IP address object connect handler address is set to NULL, which causes TCP/IP to send a TCP/IP Reset when clients attempt to connect to the TN3270 port number.

When an SNA session becomes available, the TN3270 Server reopens the listen socket by calling the socket() function. This causes the Windows NT TCP/IP driver to create a duplicate address object with a valid connect handler address. However, connection requests are validated against the old TCP/IP address object, which still has a NULL connect handler.

RESOLUTION

A hotfix for Windows NT 3.51 and 4.0 is available to correct this problem.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This problem was corrected in the latest Microsoft Windows NT 4.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K

Microsoft has confirmed this to be a problem in Windows NT version 3.51. A supported fix is now available, but has not been fully regression-tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.

Additional query words: closelistensocket prodsna snatn3270
Keywords : kbbug4.00 kbfix4.00 kbfix4.00.sp2 NTPROTOCOL NTSrvWkst nttcp kbbuglist kbfixlist
Version : 4.0
Platform : winnt
Issue type : kbbug
Solution Type : kbservicepack

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Last reviewed: December 31, 1997
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