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Q262991: All 3270 Clients Stop Responding When Snaservr.exe Starts

Article: Q262991
Product(s): Microsoft SNA Server
Version(s): WINDOWS:3.0 SP1,3.0 SP2,3.0 SP3,3.0 SP4,4.0,4.0 SP1,4.0 SP2,4.0 SP3
Operating System(s): 
Keyword(s): kbsna300sp1 kbsna300sp2 kbsna300sp3 kbsna300sp4 sna4 kbsna400sp1 kbsna400sp2 kbsna400sp
Last Modified: 08-DEC-2000

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The information in this article applies to:

- Microsoft SNA Server, versions 3.0 SP1, 3.0 SP2, 3.0 SP3, 3.0 SP4, 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3 
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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 "Request LU
Access" 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, please see the following article in the Microsoft
Knowledge Base:

  Q215838 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 "More Information" 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.

3. Start the SnaBase and SNA Server service.

4. From the server, open a new 3270 session through the SNA Server.

5. 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 this to be 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 "FastLocalRpc" registry setting. However, the
current hotfix (dated 6/6/2000 or later) does not require any registry entries.


Additional query words:

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Keywords          : kbsna300sp1 kbsna300sp2 kbsna300sp3 kbsna300sp4 sna4 kbsna400sp1 kbsna400sp2 kbsna400sp3 kbSNA400sp4fix kbSNA400PreSP4fix 
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ400 kbSNAServ300SP3 kbSNAServ300SP1 kbSNAServ400SP1 kbSNAServ400SP2 kbSNAServ400SP3 kbSNAServ300SP2 kbSNAServ300SP4
Version           : WINDOWS:3.0 SP1,3.0 SP2,3.0 SP3,3.0 SP4,4.0,4.0 SP1,4.0 SP2,4.0 SP3
Issue type        : kbbug
Solution Type     : kbfix

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