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Q226538: TCP/IP Clients Lose Connections To Multihomed SNA Server

Article: Q226538
Product(s): Microsoft SNA Server
Version(s): WINDOWS:2.0,2.1,2.11,2.11SP1,2.11SP2,3.0,3.0SP1,3.0SP2,3.0SP3,4.0,4.0SP1,4.0SP2
Operating System(s): 
Keyword(s): 
Last Modified: 12-JUN-2001

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The information in this article applies to:

- Microsoft SNA Server, versions 2.0, 2.1, 2.11, 2.11SP1, 2.11SP2, 3.0, 3.0SP1, 3.0SP2, 3.0SP3, 4.0, 4.0SP1, 4.0SP2 
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SYMPTOMS
========

Clients using TCP/IP to connect to an SNA Server are able to establish a
session, but intermittently, the client session is lost. When this happens, the
following event is logged at the server:

  Event ID: 706
  Source: SNA Server
  Description:
  Connection to client xxx.xxx.xxx.xxx:xxxx has been aborted due to too many
  (100) pending writes.

In a 3270 terminal session, users may lose their connections to the mainframe
application and be sent back to the VTAM Logon screen.

CAUSE
=====

This problem can occur if the computer running Windows NT Server has the TCP/IP
transport bound to multiple network interface cards (NICs), which are connected
to different (disparate) networks. When trying to send a message, if TCP/IP
detects a problem with the route between the server and the client, the
transport is designed to use a secondary NIC to send the message. This works
fine as long as the secondary NIC is connected to a network with a working route
to the client. But if the secondary NIC is on a disparate network, the server
message will not reach the client, causing the TCP/IP connection to timeout and
drop.

Please note that this is only one situation where an Event 706 may be generated
by Microsoft SNA Server.

RESOLUTION
==========

Disable the TCP/IP protocol binding from the adapters where it is not needed.
For example, many SNA Servers have one or more Ethernet adapters to support
TCP/IP client connections, and one or more Token Ring adapters to support DLC
connections between the server and a mainframe or AS/400. In this scenario,
because TCP/IP is not needed on the Token Ring adapter, it should be disabled
from this adapter.

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

When Microsoft Network Monitor is installed on the SNA Server, and network
traffic is captured on both NICs, you can observe the server receiving client
traffic over one card and responding back over the other card. The TCP/IP stack
switches to the alternate card when it believes the first card is busy.

For additional information about running Microsoft Windows NT Server on
multihomed computers, please see the following articles in the Microsoft
Knowledge Base:

  Q139960 Limiting LAN Traffic to One Network Adapter

  Q157025 Default Gateway Configuration for Multihomed Computers


Additional query words:

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Keywords          :  
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ300 kbSNAServ200 kbSNAServ211 kbSNAServ400 kbSNAServ210
Version           : WINDOWS:2.0,2.1,2.11,2.11SP1,2.11SP2,3.0,3.0SP1,3.0SP2,3.0SP3,4.0,4.0SP1,4.0SP2
Issue type        : kbprb

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