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Microsoft KB Archive/171942

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Knowledge Base

SNA Windows 95 and Win 3.x Named Pipe Clients Fail to Connect

Article ID: 171942

Article Last Modified on 6/28/2004


  • Microsoft SNA Server 3.0 Service Pack 4
  • Microsoft SNA Server 4.0

This article was previously published under Q171942


SNA Server Windows 95 and Windows 3.x named pipe clients may be unable to connect to an SNA Server computer if the Windows NT domain controller is slow to authenticate user logon requests.

Looking at a network monitor or sniffer trace, the trace may show the server responding repeatedly with Server Message Block (SMB) Error 231 (ERROR_PIPE_BUSY) to the client's named pipe open request (that is, SMB Open to \PIPE\COMNODE, the SNA Server named pipe, or \PIPE\COMNAP, the SnaBase named pipe).


When SNA Server named pipe clients connect to the SNA Server (or SnaBase service), the client is authenticated against a Windows NT domain controller. While this authentication is occurring, the SNA Server has no listens pending on the server end of the named pipe, causing Windows NT to respond with ERROR_PIPE_BUSY if other clients attempt to connect to the SNA Server named pipe during this time period.

The SNA Server Windows NT named pipe client accommodates this condition by retrying the named pipe open request up to 50 times with 250-millisecond delays between each request. The SNA Server Windows 95 client retries 50 times with no delay, and the Windows 3.x client only retries five times.


Microsoft has confirmed this to be a problem in SNA Server versions 3.0 and 3.0 Service Pack 1 (SP1). This problem was corrected in the latest SNA Server version 3.0 U.S. Service Pack. For information on obtaining this Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):



When the update to the SNA Server 3.0 Windows 95 and Windows 3.x clients is applied, the client retry behavior is similar to the SNA Server Windows NT client. The SNA client software should already be upgraded to 3.0 SP1 before applying this update. This has corrected this problem in SNA Server client stress testing.

However, if the Windows NT domain controller is very slow to respond to client authentication requests, the network and Windows NT domain structure should be investigated, to find ways to improve the speed of the authentication. For example, if users are connecting to an SNA Server which is separated across a wide area network from the user's Windows NT domain controller, you should consider installing a Windows NT domain controller near the SNA Server to improve responsiveness of user authentication.

Keywords: kbbug kbfix kbnetwork KB171942