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Q138269: Attachmate Extra! 3270 V4.x Causes Trap in SNA Server Service

Article: Q138269
Product(s): Microsoft SNA Server
Version(s): WINDOWS:2.0,2.1,2.11
Operating System(s): 
Keyword(s): 
Last Modified: 13-JUN-2001

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The information in this article applies to:

- Microsoft SNA Server, versions 2.0, 2.1, 2.11, on platform(s):
   - the operating system: Microsoft Windows NT 
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SYMPTOMS
========

An application exception (trap) occurs in the SNA Server service (SNASERVR.EXE)
when used with the Attachmate Extra! 3270 version 4.x emulator.

If you have Dr. Watson (DRWTSN32.EXE) configured as the default debugger, the
DRWTSN32.LOG shows an exception similar to the following:

  Application exception occurred:
  App: snaservr.DBG (pid=147)
  When: 8/1/1995 @ 16:39:1.590
  Exception number: c0000005 (access violation)

In addition, SNA Server logs Event 624 in the Windows NT Application Log (as seen
in the Event Viewer) when this trap occurs. The following is a detailed
description of the Event 624 that is logged when this trap occurs:

  Creating dump file C:\SNA\TRACES\SNADUMP.LOG for SNASERVR.EXE

  EXPLANATION
  A process (SNASERVR.EXE) ended abnormally due to a protection
  violation or similar condition and a dump file SNADUMP.LOG has been
  created that contains information about the state of the process at
  the time of the exception. Register information is contained in your
  Windows NT root directory in the file DRWTSN32.LOG.


CAUSE
=====

A 3270 emulator has two connections to the SNA Server service. One connection is
for SSCP-LU data and the other one is for PLU-SLU (Primary Logical Unit -
Secondary Logical Unit) data. The SNA Server service trap is caused because the
3270 emulator is sending a PLU-SLU message on the connection that is only meant
to handle SSCP-LU data. This is behavior which the SNA Server service is not
expecting, and it traps when it accesses its session control block for the
SSCP-LU session and treats it as a control block for the PLU-SLU session.


RESOLUTION
==========

Microsoft has modified the file, SNASERVR.EXE, to handle this error.


A 3270 emulator communicates with the SNA Server service over the Emulator
Interface Specification (EIS) interface. For performance reasons, this is a
trusted interface - that is, the SNA Server service assumes that messages across
this interface are correctly addressed and formatted. The fix for this trap
involves producing a SNA Server service which actually checks that messages
received from the emulator on the connection for SSCP-LU data are in fact valid
messages for that session, and discards them if they are not. This fix allows
the client to continue to function as if nothing had happened and it prevents
the SNA Server service from trapping.

A reproduction scenario hasn't been found to reliably cause this condition, so
the problem in the emulation is still under investigation. However, with this
update, the SNA Server now checks for this condition and no longer leads to an
application exception.


STATUS
======

Microsoft has confirmed this to be a problem in SNA Server for Windows NT. This
problem was corrected in the latest SNA Server for Windows NT, 2.11 U.S. Service
Pack. For information on obtaining the 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: prodsna 2.00 2.10 2.11 dump third-party app mainframe win3.x

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbSNAServSearch
Version           : WINDOWS:2.0,2.1,2.11
Issue type        : kbbug
Solution Type     : kbfix

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