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Q189475: Max BTU Size Limit Increased for SNA Server Connections

Article: Q189475
Product(s): Microsoft SNA Server
Version(s): WINDOWS:3.0,3.0 SP1,3.0 SP2,3.0 SP3,4.0,4.0 SP1
Operating System(s): 
Keyword(s): kbbuglist
Last Modified: 22-SEP-1999

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The information in this article applies to:

- Microsoft SNA Server, versions 3.0, 3.0 SP1, 3.0 SP2, 3.0 SP3, 4.0, 4.0 SP1 
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SYMPTOMS
========

The maximum Basic Transmission Unit (BTU) length that can be specified on a
connection has been increased to 65,536 bytes for channel connections and 32,768
bytes for non-channel connections. These are limits imposed by SNA XID formats,
which allow 2 bytes for maximum BTU size for channel connections and 15 bits for
non-channel connections.

CAUSE
=====

The maximum BTU length was previously hardcoded for a maximum length of 16,393
bytes, which is the largest size supported by Token Ring networks.

RESOLUTION
==========

Microsoft has confirmed this to be a problem in SNA Server versions 3.0, 3.0
SP1, 3.0 SP2, 3.0 SP3, 4.0, and 4.0 SP1. We are researching this problem in SNA
Server version 3.0 and will post more information here in the Knowledge Base as
it becomes available.

This problem was corrected in the latest SNA Server version 4.0 U.S. Service
Pack. For information on obtaining this Service Pack, query on the following
word in the Microsoft Knowledge Base (without the spaces):

  S E R V P A C K


MORE INFORMATION
================

Setting the maximum BTU length to the limit does not guarantee that the SNA
Server connection will actually use this value. The individual link service or
the host can negotiate it down. For information on how the actual Max BTU value
is determined for 802.2 DLC connection, refer to the following Knowledge Base
article:

  Q148972 How SNA Server Determines Max BTU Over 802.2 DLC

Additional query words: snacfg

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Keywords          :  kbbuglist
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ300 kbSNAServ400 kbSNAServ300SP3 kbSNAServ300SP1 kbSNAServ400SP1 kbSNAServ300SP2
Version           : WINDOWS:3.0,3.0 SP1,3.0 SP2,3.0 SP3,4.0,4.0 SP1
Issue type        : kbbug
Solution Type     : kbfix

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