Microsoft KB Archive/275469

= APPC Load Balancing May Fail to Choose &quot;Best&quot; SNA Server =

Article ID: 275469

Article Last Modified on 2/22/2007

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APPLIES TO


 * Microsoft Host Integration Server 2000 Standard Edition
 * Microsoft SNA Server 4.0 Service Pack 3
 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 4.0 Service Pack 1
 * Microsoft SNA Server 4.0 Service Pack 2

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This article was previously published under Q275469



SYMPTOMS
An Advanced Program-to-Program Communications (APPC) or Common Programming Interface for Communications (CPI-C) application may not connect to a SNA Server that has the best chance of providing a LU 6.2 session over the specified APPC Local LU/RemoteLU/Mode. As a result, the application may not be able to obtain an available LU 6.2 session or the application may experience a delay while finding a SNA Server with an available LU 6.2 session.

The symptoms that are experienced by an end user who is running the APPC or CPI-C application may vary.



CAUSE
The APPC library locates an available LU 6.2 session that matches the parameters (Local APPC LU and Remote APPC LU, for example) that are requested by the application. If there are multiple SNA Server computers that can provide the requested Local and/or Remote APPC LUs, the APPC Library contacts the SNA Server computers in a random order according to how the servers are listed in the SNA Client's Service Table. The SNA Server computer can respond to the session requests with various errors depending on the state of its configured connections and the availability of the LU 6.2 sessions on those connections.

When the APPC Library receives these error responses from the available SNA Server computers, the errors are ranked to determine which SNA Server computer has the greatest probability of providing the requested LU 6.2 session.

The problem described here occurs because the errors that are returned by the SNA Servers are giving priority to SNA Servers that have a lower chance of being able to satisfy the session request than other SNA Servers that have a better chance of satisfying the request.

NOTE: This problem occurs only when the application specifies a specific Local APPC LU in the TP_STARTED request. If the application specifies a &quot;blank&quot; Local APPC LU in the TP_STARTED request, this problem does not occur.



RESOLUTION
To resolve this problem, obtain the latest service pack for SNA Server 4.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack



STATUS
Microsoft has confirmed that this is a problem in Microsoft SNA Server version 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3.

This problem was first corrected in SNA Server 4.0 Service Pack 4.

Additional query words: HIS 2000

Keywords: kbbug kbfix kbqfe kbsna400presp4fix kbsna400sp4fix KB275469

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