SNA Server LU Allocation Favors Active Remote Connections over Available Local Connections

ID: Q236591

The information in this article applies to:
IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SUMMARY

In the following scenario, two SNA Servers are deployed, SNAS1 (primary) and SNAS2 (backup). SNAS1 is geographically local to the client and SNAS2 is geographically remote from the client. Both SNA Servers share the same domain and organization-wide TN3270 LU pool.

The PU on SNAS1 undergoes a scheduled or unscheduled recycle and recovers to return to an active/available status. During this period of downtime, a new client request for a session is serviced by SNAS2, and thereafter, the following behavior may be observed:

Although this behavior is by design, there have been requests to support an option for TN3270 that allocates sessions across restarted/recovered local connections in preference to remote connections.

NOTE: This feature does not provide TN3270 client load balancing across more than one TN3270 server. That function must be provided by the TN3270 client or possibly the TCP/IP name service being used. If this functionality is needed, SNA Server provides transparent client load balancing across SNA Server computers using its native 3270 interface. For additional information about SNA Server load balancing, please see the following articles in the Microsoft Knowledge Base:
Q185446 TN3270 Server LUA Pool Use Should Load Balance Across Servers
Q128244 SNA Server Load Balancing and Hot Backup
For additional information about shared LUA pool use by more than one TN3270 server, please see the following article in the Microsoft Knowledge Base:
Q182139 LUA Pool Cannot Be Assigned to Two TN3270 Servers
WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys and Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).


After this update is applied to the SNA Server, this new behavior for TN3270 (LUA/3270 application) resource location is enabled by setting the ResLocFlags registry entry to a DataValue of either 0x8000 or 0x8001 under:
KEY_LOCAL_MACHINE\System\CurrentControlSet\Services \TN3270\Parameters ResLocFlags: REG_DWORD,default = 0
If the DataValue is 0x8000, then all Open(SSCP) messages are first sent to the local SNA Server even if an existing connection is open to a remote server.

If the DataValue is 0x8001, it enables both the "try local first" and the "load balance amongst remote servers" feature as detailed in article Q185446.

In both cases, the SNA Server first tries to use local resources; if a request cannot be satisfied locally, it uses a remote resource. There is no load balancing among local SNA Servers, that is, the TN3270 Server first consumes all resources from one local SNA server before allocating resources from the other local SNA servers.

NOTE: The default behavior is to always use an existing active connection first.

After this update is applied and the ResLocFlags entry is set, the SnaBase service and TN3270 service must be restarted for the change to take effect.


MORE INFORMATION

This supported feature is now available from Microsoft, but has not been fully regression tested and should be applied only to systems having a specific need for it. If you are not severely affected by the lack of this feature, Microsoft recommends that you wait for the next Microsoft SNA Server version 4.0 service pack that contains this feature.

To obtain this feature immediately, contact Microsoft Product Support Services. 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 feature should have the following file attributes or later:

File name Date Time
Snadmod.dll 06/02/99 15:40

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 feature, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this feature, and if it is determined that you only require the feature 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

Additional query words: 


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

Last Reviewed: July 7, 1999