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Q311438: SNA Applications "Hang" with Event 556

Article: Q311438
Product(s): Microsoft SNA Server
Version(s): 4.0
Operating System(s): 
Keyword(s): kbDSupport sna4 kbsna400sp1 kbsna400sp2 kbsna400sp3 kbhis2000 kbhis2000bug kbsna400sp4
Last Modified: 08-MAY-2002

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The information in this article applies to:

- Microsoft Host Integration Server 2000 
- Microsoft SNA Server, version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

SNA applications that are running on an SNA Client may stop responding ("hang"),
when one of the applications requests a logical unit (LU). The following event
may be logged in the Application Event Log when this occurs:

  Event ID: 556
  Description: A system error occurred while making a pipe connection, rc =
  <return code>

This problem occurs when there are multiple SNA applications running on the same
system that repeatedly load and unload any of the SNA API (RUI, SLI, APPC, or
CPI-C) dynamic link libraries (DLLs).

CAUSE
=====

An internal resource that keeps track of SnaBase's active RamPipe connections
can exceed its maximum value under certain circumstances, which causes the
problem.

RESOLUTION
==========

SNA Server 4.0
--------------

A supported fix is now available from Microsoft, but it is only intended to
correct the problem described in this article and should be applied only to
systems experiencing this specific problem. This fix may receive additional
testing at a later time, to further ensure product quality. Therefore, if you
are not severely affected by this problem, Microsoft recommends that you wait
for the next Microsoft SNA Server version 4.0 service pack that contains this
fix.

To resolve this problem immediately, contact Microsoft Product Support Services
to obtain the fix. For a complete list of Microsoft Product Support Services
phone numbers and information about support costs, please go to the following
address on the World Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are normally incurred for support calls may
be canceled, if a Microsoft Support Professional determines that a specific
update will resolve your problem. Normal support costs will apply to additional
support questions and issues that do not qualify for the specific update in
question.

The English version of this fix should have the following file attributes or
later:

+---------------------------------+
| File name   | Date      | Time  | 
+---------------------------------+
| Snadmod.dll | 3/26/2001 | 11:28 | 
+---------------------------------+

NOTE: Because of file dependencies, the most recent fix that contains the above
files may also contain additional files.



Host Integration Server 2000
----------------------------

No fix is available for this problem in Host Integration Server 2000 at this
time.

WORKAROUND
==========

To avoid this problem, keep the number of concurrent SNA applications below 15
or rewrite the applications to avoid repeatedly loading and unloading the SNA
API DLLs.

STATUS
======

SNA Server 4.0

Microsoft has confirmed this to be a problem in Microsoft SNA Server version
4.0.

Host Integration Server 2000

Microsoft has confirmed this to be a problem in Microsoft Host Integration Server
2000.


MORE INFORMATION
================

SnaBase maintains an internal table called the LPd table to track client server
connections. This table can contain up to 255 entries. If there are multiple
processes that repeatedly load and unload any of the SNA API DLLs, each process
may consume as many SnaBase LPd records as there are processes. For example, if
you have 30 processes, the total number of allocated LPds can be up to 30*30,
which is greater than 255. How many records each process actually uses depends
on the sequence in which they load/unload the SNA API DLLs. If the timing is
correct each process may only use one record; if the timing is bad, each process
can consume a lot more. There must least 15 local SNA processes in order for
this problem to occur.


Additional query words:

======================================================================
Keywords          : kbDSupport sna4 kbsna400sp1 kbsna400sp2 kbsna400sp3 kbhis2000 kbhis2000bug kbsna400sp4 
Technology        : kbAudDeveloper kbSNAServSearch kbHostIntegServ2000 kbSNAServ400
Version           : :4.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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