Microsoft KB Archive/195818

= Windows NT 4.0 Service Pack 4 Breaks SNA Encrypted Client Connectivity =

Article ID: 195818

Article Last Modified on 10/27/2006

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APPLIES TO


 * Microsoft SNA Server 3.0 Service Pack 4
 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 3.0 Service Pack 2
 * Microsoft SNA Server 3.0 Service Pack 3
 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 4.0 Service Pack 1

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This article was previously published under Q195818





SYMPTOMS
After you upgrade SNA Server (version 3.0 or 4.0) to Windows NT 4.0 Service Pack 4, any SNA user configured to use data encryption will be unable to establish a session through the server when connecting from the following client platforms:


 * Windows NT 4.0 Service Pack 3 or earlier (running the SNA 3.0 or 4.0 Windows NT, SNA Windows 9x or SNA Windows 3.x client software)
 * Windows 98 or Windows 95 (running the SNA 3.0 or 4.0 Windows 9x client software)
 * Windows 3.x (running the SNA 3.0 or 4.0 Windows 3.x client software).

SNA Windows NT clients that are upgraded to Windows NT 4.0 Service Pack 4 will be able to connect to an SNA Server which has also been upgraded to Windows NT 4.0 Service Pack 4.

Likewise, if an SNA Windows NT client computer is upgraded to Windows NT 4.0 Service Pack 4, the SNA client user (when configured to use data encryption) will be unable to establish a session through SNA Server if the server is running Windows NT 4.0 Service Pack 3 or earlier.

The following symptoms will occur when clients experience this problem:


 * The SNA Windows NT or Windows 3.x 3270 applet displays the following error on startup, and fails to display a 3270 session list within the Session Configuration dialog box. ERROR - Reading SNA Server Configuration
 * The SNA Windows NT or Windows 3.x 5250 applet displays the following error when attempting to open a session, and will fail to retrieve Remote APPC LU aliases within the Session Configuration dialog box: WIN5250 SNA Server has been deactivated. Contact System Administrator [F003][010000F0] -or- The Remote LU name specified for this session is invalid [0001] [0000001B]
 * The SNA Windows NT client logs Event 705 to the Windows NT Application Event log: Event ID: 705 Source: SNA 3270 Emulator (or) SNA APPC Application Description: Logon Failed. EXPLANATION Connection request failed due to data security Access denied -- required data encryption -- Error Code: 43
 * The SNA Windows 95 3270 applet displays the LU name in the session configuration dialog box, but stops responding (hangs) with a blank screen when attempting to connect to the session.
 * When the SNA Windows 95 client fails to connect, the SNA Server logs Event 717 to the Windows NT Application Event log: Event ID: 717 Source: SNA Base Service Description: Client-Server Connection Disconnected. EXPLANATION Security Error - unable to decode security messages. Error Code = 0x8009030f



CAUSE
The Microsoft Windows NT 4.0 Service Pack 4 (SP4) NTLM security package modifies the implementation of the encryption context options for applications which use the InitializeSecurityContext API. This causes SNA Server (and SNA Windows NT and Windows 9x clients) to build encrypted messages differently when running on Windows NT 4.0 SP4 than for prior Windows NT versions. This causes interoperability problems between SNA clients and servers that are running on different versions of Windows NT when encryption is enabled for an SNA user.



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

SNA Server 4.0
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



WORKAROUND
To work around this problem, disable the use of SNA Server client-server encryption until SNA Server, SNA client, and/or Windows NT software can be upgraded within the network.



STATUS
Microsoft has confirmed this to be a problem in the products listed at the beginning of this article when running on a mixture of Windows NT 4.0 SP4 and prior Windows NT versions. This problem was first corrected in SNA Server 3.0 Service Pack 4.



MORE INFORMATION
The following implementation decisions must be made to fully resolve this issue and support client encryption with mixed SNA Server, SNA client, and Windows NT versions:


 * If SNA Servers are to be upgraded to Windows NT 4.0 SP4, before any SNA clients are upgraded to Windows NT 4.0 SP4, the SNA Server update should be applied to the servers first, to preserve connectivity for back-level clients (including SNA Windows 9x and Windows 3.x clients which are not running on Windows NT).
 * If SNA Windows NT (or SNA Windows 9x) clients are to be upgraded to Windows NT 4.0 SP4, before the SNA Servers are upgraded to Windows NT 4.0 SP4, the SNA client update should be applied to the clients, to preserve connectivity to back-level servers.
 * Applying the SNA update simultaneously to all SNA Servers and SNA clients preserves interoperability regardless of Windows NT versions being used.

The following tables summarize interoperability between various combinations of SNA Server, SNA client, and Windows NT software.

Old SNA CLIENT or Old SNA Server software = SNA 3.0 (including Service Packs 1-3), SNA 4.0 (including Service Pack 1)

New SNA Client or New SNA Server = SNA 3.0 (post-Service Pack 3), SNA 4.0 (post-Service Pack 1)

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Old SNA       ********** Old SNA Server ******* Client        on NT4SP3 or earlier   on NT4SP4 -

NT4SP3, SNA NT or            WORKS             FAILS SNA Win9x

NT4SP4, SNA NT or            FAILS             WORKS SNA Win9x

Win9x, SNA Win9x            WORKS             FAILS

Any Platform, SNA Win3x            WORKS             FAILS

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Old SNA       ********** New SNA Server ******* Client        on NT4SP3 or earlier   on NT4SP4 -

NT4SP3, SNA NT or            WORKS             WORKS SNA Win9x

NT4SP4, SNA NT or            FAILS             FAILS SNA Win9x

Win9x, SNA Win9x            WORKS             WORKS

Any Platform, SNA Win3x            WORKS             WORKS

 New SNA       ********** Old SNA Server ******* Client        on NT4SP3 or earlier   on NT4SP4 -

NT4SP3, SNA NT or            WORKS             FAILS SNA Win9x

NT4SP4, SNA NT or            WORKS             FAILS SNA Win9x

Win9x, SNA Win9x            WORKS             FAILS

Any Platform, SNA Win3x            WORKS             FAILS

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New SNA       ********** New SNA Server ******* Client        on NT4SP3 or earlier   on NT4SP4 -

NT4SP3, SNA NT or            WORKS             WORKS SNA Win9x

NT4SP4, SNA NT or            WORKS             WORKS SNA Win9x

Win9x, SNA Win9x            WORKS             WORKS

Any Platform, SNA Win3x            WORKS             WORKS

Keywords: kbbug kbfix KB195818

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