Microsoft KB Archive/183791

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APPC/CPI-C Program Unexpectedly Hangs Through SNA Server 4.0

Article ID: 183791

Article Last Modified on 10/27/2003


  • Microsoft SNA Server 4.0

This article was previously published under Q183791


An APPC or CPI-C application may unexpectedly hang while sending data on an active conversation to a partner program running on a remote system. This problem only occurs with SNA Server 4.0.

This problem only occurs when the remote system has initiated the LU6.2 session by sending a BIND to SNA Server that contains either a Length- Checked Compression control vector (key 0x66) or Fully Qualified PCID control vectors (key 0x60), or both. The format of the SNA BIND command and control vectors can be found in the following IBM reference:

IBM SNA Formats Guide, IBM part number: GA27-3136:

  • For BIND command format, see Chapter 5, "Request/Response Units (RUs)".
  • For control vector formats, see Chapter 8, "Common Fields".


If SNA Server 4.0 receives an LU6.2 BIND request that contains a compression control vector or fully qualified PCID control vector, this could corrupt internal SNA client-server credit settings. This could cause the SNA Server client APPC interface to stop sending requests to SNA Server after several hundred messages are sent.


Reconfigure the remote system so that it does not initiate any LU6.2 sessions, and change SNA Server so that it always initiates the LU6.2 session. In SNA Server, automatic LU6.2 session activation can be accomplished by configuring a non-zero automatic activation limit on the APPC mode entry, and partnering the Local APPC LU with the Remote APPC LU that the APPC or CPI-C application will be using.


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


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