HIS 2000 Client LU6.2 load balancing across SNA Server services (266275)

Important This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SUMMARY

An APPC or CPIC application running on Host Integration Server (as in SNA Server 4.0) directs Allocate requests for a specific LU/LU pair against the same SNA Server service. When an APPC or CPIC application gets a conversation through a specific SNA Server, further Allocate requests for the same LU/LU pair favors the same server.

However, in Host Integration Server, a registry entry can be used to force APPC or CPIC Allocate requests from a single process through different SNA Servers in the subdomain. You can use this to achieve load balancing of LU6.2 requests from a single APPC or CPIC process to two or more SNA Server services configured with redundant APPC LU resources. Also, if an LU6.2 application has a conversation through a remote server and a local server service (providing the same resources) is started, the registry entry can cause the LU6.2 application to try the local server for new Allocate requests.

For more information about APPC load balancing with SNA Server (all versions) and Host Integration Server (when the registry setting is not used), click the following article number to view the article in the Microsoft Knowledge Base:

128244 SNA Server load balancing and hot backup

MORE INFORMATION

The TN3270 load-balancing enhancements implemented in SNA Server 4.0 Service Pack 3 (described in knowledgebase article Q236591) have now been implemented for APPC/LU6.2 in Host Integration Server. This new LU6.2 load-balancing feature is not available in SNA Server 4.0.

This new behavior for CPIC or APPC application resource location is enabled by setting the ResLocFlags registry entry to a Data value of either 0x8000 or 0x8001 under the following registry key:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\SnaBase\Parameters\Client\ ResLocFlags: REG_DWORD: 0x8001 (Default = 0)

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If the data value is 0x8000, then the APPC DLL routes all Allocate requests to any locally running instances of the SNA Server service (for example, if the LU6.2 application is running on a server), instead of trying an existing connection to SNA Server running on a separate computer.

If the data value is 0x8001, the "try local first" behavior is implemented, as well as the "load balance among remote servers" feature. which is described in article Q185446.

In both cases, the Host Integration Server APPC DLL first tries to use a locally running SNA Server service (if running on a server). If a request cannot be satisfied locally, the APPC DLL tries to connect to a remote server that supports the LU/LU/mode being requested. Note that there is no load balancing among local SNA Servers. That is, APPC or CPIC applications will first consume all resources from one local SNA server before allocating resources from the other local SNA Servers.

NOTE: If ResLocFlags is not set, it defaults to 0, meaning that the behavior in SNA Server 4.0 is used. When the APPC DLL gets a conversation through one SNA Server, it tries the same SNA Server for additional Allocate requests for the same LU/LU pair. The APPC DLL will not try an additional SNA Server until the first server's LU6.2 resources are exhausted or the server becomes unreachable.