Microsoft KB Archive/216047

= Activating Numerous DLC Connections Results in Inactive LUs =

Article ID: 216047

Article Last Modified on 9/22/2005

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APPLIES TO


 * Microsoft SNA Server 3.0 Service Pack 4
 * Microsoft SNA Server 4.0

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This article was previously published under Q216047



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



SYMPTOMS
An SNA Server that has numerous DLC 802.2 connections may experience symptoms similar to the following if the connections are activated concurrently:

 All of the connections are in an Active state, but some of the connections have Inactive 3270 Logical Units (LUs). Some of the connections stay in an Inactive state. The Windows NT application event log contains numerous occurrences of the following message:

Event ID: 266

Source: SNA DLC Link Service

Description: The DLC 802.2 link service could not allocate a DLC buffer for an outgoing message, message type 16.



The number of connections that can be activated before experiencing this problem will vary. In general, this may occur in environments that have 50 or more DLC 802.2 connections where each connection has many 3270 LUs defined.



CAUSE
The SNA Server DLC 802.2 link service uses an internal buffer pool to handle messages that it has to process. If this buffer pool is exhausted, the link service may discard some of the messages that is it receiving from the SNA Server service or from the DLC protocol stack. If the link service discards these messages, the symptoms described above can occur.



SNA Server 4.0
To resolve this problem, obtain the latest service pack for SNA Server version 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

SNA Server 3.0
To resolve this problem, obtain the latest service pack for SNA Server version 3.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

184307 How to Obtain the Latest SNA Server Version 3.0 Service Pack



STATUS
Microsoft has confirmed that this is a problem in Microsoft SNA Server versions 3.0, 3.0 SP1, 3.0SP2, 3.0 SP3, 4.0, 4.0 SP1, 4.0 SP2. This problem was first corrected in SNA Server version 3.0 Service Pack 4 and SNA Server version 4.0 Service Pack 3.



MORE INFORMATION
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

By default, the size of the internal buffer pool used by the DLC 802.2 link service is 1 MB (1,024,000 bytes). SNA Server 3.0 Service Pack 1 and later allows this buffer pool to be increased by adding the following Registry parameter: 

HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/ /Parameters/ExtraParameters/LlcBufferPoolSize

is the name of the DLC 802.2 link service (that is, snadlc1) that the buffer pool is being increased for.

This parameter may need to be increased on SNA Servers that have a large number of DLC 802.2 connections and 3270 LUs. This buffer can be exhausted by simultaneously starting a large number of these connections because of the large number of messages that have to be processed by the link service during the startup sequence. The following is a list of messages that have to be processed by the link service when connections containing 3270 LUs are started:
 * XID exchanges
 * ACTPU (Activate PU) and ACTPU Responses for each per connection
 * ACTLU (Activate LU) and ACTLU Responses for each LU on each connection
 * Notify and Notify Responses for each LU on each connection

After applying the update, the DLC 802.2 link service will allocate additional memory outside of the LLC buffer pool whenever this buffer pool is exhausted. This prevents the case where the link service discards messages when the buffer pool is exhausted. It is recommended that the LLC buffer pool is large enough to prevent the allocation of memory outside of this pool under normal operating conditions as using memory outside the LLC buffer pool for transmit buffers effects performance to some extent.

For additional information about another DLC 802.2 link service problem related to exhausting the LLC buffer pool, please see the following article in the Microsoft Knowledge Base:

198398 AccessViolation in Snalink.exe Activating Numerous Connections

The previously referenced article also includes information on how to add and change the LLCBufferPoolSize registry parameter.

Keywords: kbbug kbfix kbsna300sp4fix kbsna400sp3fix kbqfe kbhotfixserver KB216047

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