Microsoft KB Archive/150569

= Stardata TSR on Win3.x Client Causes SNABase Service to Loop =

Article ID: 150569

Article Last Modified on 11/26/2003

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APPLIES TO


 * Microsoft SNA Server 2.0, when used with:
 * Microsoft Windows NT 4.0
 * Microsoft SNA Server 2.1, when used with:
 * Microsoft Windows NT 4.0
 * Microsoft SNA Server 2.11 Service Pack 1, when used with:
 * Microsoft Windows NT 4.0

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This article was previously published under Q150569





SYMPTOMS
SNABase service will reach approximately 100% CPU utilization in Performance Monitor and all SNA Server clients connected to this SNA Server will be disconnected.



CAUSE
A badly written application running on a Windows 3.x computer overwrites the memory address occupied by the SNA Server Win3.x client-server interface DLL files. If the bad application hits a particular code segment (owned by the SNA Server components), it will cause SNA Server Win3.x client-server interface to send a bogus service table update to the SNA Server with the bad application's data. This causes the SNABase service running on the SNA Server to reach approximately 100% CPU utilization.

NOTE: Service table updates will normally flow from an SNA Server Win3.x client only when the client is configured to support the registration of an APPC invokable TP.



WORKAROUND
A fix was made to SNA Server:  To cause verbose validity checking on any incoming service table update (msgtype 07); only the expected service table updates will be processed.

In addition, the following application event will be logged when SNA Server receives a bad service table update from a client:

631 - Invalid message received across the LAN.

 To ignore any incoming service table update.

To cause SNA Server to ignore all incoming service table updates, set the following parameter: \hkey_local_machine \system \current_control_set \Services \SNABase\ \parameters: IgnoreClientUpdates:REG_DWORD:1 If this parameter has any non-zero value, the SNABase will ignore all client updates.

It will also log event 709 when it receives one.

NOTE: If this parameter is set up to ignore all incoming service table updates, a SNA Server Windows NT client running SNA Admin will not be able to administer the domain. Therefore, it is recommended that you not set this for IgnoreClientUpdates unless it is determined that verbose validity checking is not preventing the problem.



STATUS
Microsoft has confirmed this to be a problem in Microsoft SNA Server versions 2.0, 2.10, 2.11, and 2.11.sp1. This problem was corrected in the latest Microsoft SNA Server 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

Keywords: kbbug kbnetwork KB150569

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