SNA Server Logs Events 684 and 685 When Using SDLC Connection (176849)

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:

139594 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