Microsoft KB Archive/255173

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Article ID: 255173

Article Last Modified on 6/29/2004


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

This article was previously published under Q255173


When a user tries to connect a TN3270E session using the 3270 Applet included with SNA Server, the applet may stop responding with a blank screen. The Status bar shows Connected. At this point, the applet is locked, and the only way to close the session is to end the task using Task Manager. This problem only occurs when the 3270 Applet is configured in TN3270E mode.


When the BIND sent from the host specifies a Max Request Unit (RU) size of 0 for the primary half-session, the 3270 Applet moves into a tight loop while processing the BIND.


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


Microsoft has confirmed that this is a problem in SNA Server versions 3.0 (all SP), 4.0, 4.0SP1, 4.0SP2, and 4.0SP3.

This problem was first corrected in SNA Server 4.0 Service Pack 4.


The following excerpt from an SNA Server message trace shows a BIND sent from the host specifying an RU size of 0 for the primary half-session:

DLC 07160000->01020101 DLC DATA
DLC DAF:02 OAF:01 ODAI:off Exp.
DLC ---- Header at address 01204688, 1 elements ----
DLC 01020000 00002D00 02012757 01006C06 ......-...'W..l.
DLC ---- Element at address 01BF0EDC, start 10, end 49 ----
DLC 6B800031 010303B1 B0308000 00850000 k..1.....0...e..
DLC 00028000 00000000 00000002 000008D9 ...............R

Bytes 10 and 11 (where Byte 0 is X'31') in this BIND are defined as X'8500'. These are the bytes that specify the RU sizes for the secondary and primary half-sessions, respectively. When the primary half-session Max RU size is 0, the applet gets into a tight loop when it receives the BIND Image in TN3270E mode. The updated TN3270.DLL corrects the problem in the applet. Also, if the BIND is changed so that Byte 11 is not 0, the problem does not occur.

Third-party emulators may also experience this problem, and it may be necessary to upgrade to a newer version. Please refer to the vendor of the emulator for more information.

Keywords: kbbug kbfix kbsna400presp4fix kbqfe kbsna400sp4fix KB255173