Microsoft KB Archive/262991

= All 3270 Clients Stop Responding When Snaservr.exe Starts =

Article ID: 262991

Article Last Modified on 7/15/2004

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APPLIES TO


 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 3.0 Service Pack 2
 * Microsoft SNA Server 3.0 Service Pack 3
 * Microsoft SNA Server 3.0 Service Pack 4
 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 4.0 Service Pack 1
 * Microsoft SNA Server 4.0 Service Pack 2
 * Microsoft SNA Server 4.0 Service Pack 3

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This article was previously published under Q262991



SYMPTOMS
When the SNA Server service Snaservr.exe is started or restarted, all 3270 clients may stop responding with a black screen while attempting to open a new session through the server. A similar problem can affect LUA or APPC applications, if the LUA or APPC security feature is enabled in the SNA Server subdomain's Security folder. If APPC security is enabled and this problem occurs, the APPC application's [MC_]ALLOCATE request stops responding indefinitely. If LUA security is enabled and this problem occurs, the LUA application's RUI_INIT or SLI_OPEN does not complete.



CAUSE
This problem occurs if the server-side SnaBase service receives more than 256 concurrent client sponsor connections before the SNA Server service attempts its first RPC communication to the local SnaBase service. When a 3270 client attempts to open a session through SNA Server, SNA Server sends a &quot;Request LU Access&quot; RPC request to the local SnaBase service to verify that the user has permissions to open the session. However, if there are already over 256 client connections to SnaBase, the server never receives the reply due to a problem with internal addressing of messages on the server.



RESOLUTION
To resolve this problem, obtain the latest service pack for SNA Server 4.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack

This update is intended for systems running Microsoft SNA Server 4.0 Service Pack 3. In addition to this update, see the &quot;More Information&quot; section of this article for information on the registry value that must also be applied.



WORKAROUND
The following procedure ensures that the SNA Server service does not encounter this problem after its started. This procedure assumes that Ethernet and/or Token Ring are being used to connect to the SNA client computers, and a separate Ethernet or Token Ring adapter is being used for SNA DLC connectivity.


 * 1) Stop the SnaBase service on the server.
 * 2) Disconnect the Ethernet cable(s), which connects the SNA Server with the client network(s). All host network connections need to be attached.

NOTE: If SnaBase, SNA Server, or SNA link services are configured to run under a user account, unplugging the LAN cable causes these services to fail to be validated by a domain controller. Therefore, these services need to be changed to run under the Local System account before this step is performed.
 * 1) Start the SnaBase and SNA Server service.
 * 2) From the server, open a new 3270 session through the SNA Server.
 * 3) Reconnect the network cable(s) so that clients can now connect to SNA Server.

NOTE: If a single Token Ring or Ethernet adapter is being used for client and SNA connectivity, the SnaBase service fails to restart in step 3. Therefore, you need to disconnect client connectivity from the hub, switch, or router when you perform this procedure.



STATUS
Microsoft has confirmed that this is a problem in Microsoft SNA Server 3.0 (all service packs), and SNA Server 4.0, 4.0 SP1, 4.0 SP2 and 4.0 SP3.

This problem was first corrected in SNA Server 4.0 Service Pack 4.



MORE INFORMATION
To correct this problem, apply the hotfix described in the previous section.

NOTE: The initial version of this hotfix (dated 5/2/2000 or 5/18/2000) required the manual configuration of a &quot;FastLocalRpc&quot; registry setting. However, the current hotfix (dated 6/6/2000 or later) does not require any registry entries.

Keywords: kbbug kbfix kbsna400presp4fix kbqfe kbsna400sp4fix KB262991

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