Q176849: SNA Server Logs Events 684 and 685 When Using SDLC Connection

Article: Q176849
Product(s): Microsoft SNA Server
Version(s): WINDOWS:2.0,2.1,2.11,2.11 SP1,2.11 SP2,3.0,3.0 SP1,3.0 SP2
Operating System(s): 
Keyword(s): kbbuglist
Last Modified: 12-JUN-2001

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The information in this article applies to:

- Microsoft SNA Server, versions 2.0, 2.1, 2.11, 2.11 SP1, 2.11 SP2, 3.0, 3.0 SP1, 3.0 SP2 
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SYMPTOMS
========

An SNA Server computer using an SDLC Link Service for host connections may log
the following message in the Windows NT application event log at random
intervals:

  Event ID: 684
  Description: A buffer pool audit has been triggered by a pool extension.

The description also lists the number of allocated trusted headers. Each
successive Event 684 shows a larger number of allocated trusted headers.

Eventually the allocated trusted headers will reach the maximum value, and the
connection to the host will be lost. At this point, the following message will
be logged in the application event log:

  Event ID: 685
  Description: An attempt was made to extend a buffer pool, but the
  related pool had reached its maximum size. The affected component is
  terminating, and an audit of the buffer pools just before termination is
  attached.

  <Listing of the buffer pools omitted>

A trace of the SDLC Link Service shows numerous DLCST UPSN messages (update
station statistics) being sent to the SNA Server service. For more information
about DLCST UPSN messages, refer to the following Microsoft Knowledge Base
article:

  Q139594 Meaning of "DLCST UPSN" in an SNA Server Data Link Control Trace

CAUSE
=====

Messages from the Link Service are being placed into the buffer pool much faster
than the SNA Server service can process them. This is usually caused by a
problem elsewhere in the system, for example, in the SDLC adapter or driver.
However, SNA Server should deal with this situation without dropping the host
connection.

The UPSNSTAT messages let the SNA Server service track statistics for sending in
RECFMS messages to the host. RECFMS has been retired from SNA for type 2 nodes,
and UPSNSTAT is not in the published Microsoft SNA Device Interface
Specification, so UPSNSTAT message handling has been removed from the
Ibmsdlc.dll Link Service. This eliminates the effects of the problem.

STATUS
======

Microsoft has confirmed this to be a problem in SNA Server version 3.0 Service
Pack 2 and earlier.

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):

  S E R V P A C K

Additional query words:

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Keywords          :  kbbuglist
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ300 kbSNAServ200 kbSNAServ211 kbSNAServ210 kbSNAServ211SP1 kbSNAServ211SP2 kbSNAServ300SP1 kbSNAServ300SP2
Version           : WINDOWS:2.0,2.1,2.11,2.11 SP1,2.11 SP2,3.0,3.0 SP1,3.0 SP2
Issue type        : kbbug
Solution Type     : kbfix

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