SNA Server Drops Client LAN Connection, Logs Event 631 on DEC Alpha

ID: Q235849

The information in this article applies to:

SYMPTOMS

If an SNA application is running on a DEC Alpha processor, on either SNA Server or an SNA Server Windows NT client, the client-server LAN session may unexpectedly stop responding (hang) with the following event

Event ID: 631
Source: SNA Server (or SNA Application)
Description: Invalid message received across the LAN: remote: (IP address):1477 Bad sequence number 183 (expected 184)
where the expected sequence number may be one less or one more than expected. If this occurs while an APPC application is sending or receiving data, the APPC application may hang unexpectedly, or receive the following APPC error message:
primary_rc = F003 (AP_COMM_SUBSYSTEM_ABENDED)
The Event 631 may be logged on the DEC Alpha computer where the SNA Server or SNA client software is running, or on a separate SNA Server or SNA client computer that is communicating to the DEC Alpha computer.


CAUSE

If SNA Server data is being sent and received simultaneously over a single client-server LAN connection (to or from one client), internal "send sequence number" and "receive sequence number" variables may be incremented from different threads at the same instant. If this timing condition occurs on a DEC Alpha computer, one sequence number may fail to be updated, causing SNA Server to incorrectly detect an out-of-sequence message. These sequence number variables occur on consecutive BYTE boundaries within a non-packed structure. The DEC Alpha appears to improperly lock one of the BYTE values during a increment operation on an adjoining, separate BYTE value, preventing it from being updated.


RESOLUTION

A supported fix that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next SNA Server 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 on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp
The English version of this fix should have the following file attributes or later (for DEC Alpha processors only):

File name Date Time
Snadmod.dll 06/09/99 06:51p
Snabase.exe 06/09/99 06:56p
Snaip.dll 06/09/99 06:54p
Snalm.dll 06/09/99 06:54p
Snanw.dll 06/09/99 06:53p

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

NOTE: If this product was already installed on your computer when you purchased it from the Original Equipment Manufacturer (OEM) and you need this fix, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this fix, and if it is determined that you only require the fix you requested, no fee will be charged. However, if you request additional technical support, and if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support, you may be charged a non-refundable fee.

For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base:
Q154871 Determining If You Are Eligible for No-Charge Technical Support


STATUS

Microsoft has confirmed this to be a problem in SNA Server 4.0, 4.0 SP1 and 4.0 SP2.


MORE INFORMATION

SNA Server has worked around this problem by adding 7 pad bytes between the send and receive sequence number (BYTE) values, which forces these counters to fall on separate DWORD (8 byte) boundaries within memory. With these extra pad bytes, the Event 631 problem no longer occurs.

Additional query words: 


Keywords          : sna4 sna4sp1 sna4sp2 
Version           : WINDOWS:4.0,4.0 SP1,4.0 SP2
Platform          : WINDOWS 
Issue type        : kbbug

Last Reviewed: July 23, 1999