Microsoft KB Archive/175321

= SNA Client Sessions Hang until SNA Server is Restarted =

Article ID: 175321

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Server 4.0, Terminal Server Edition
 * Microsoft Windows NT Server 3.51
 * Microsoft Windows NT Server 4.0 Standard Edition
 * Microsoft SNA Server 3.0
 * Microsoft SNA Server 2.11 Service Pack 1
 * Microsoft SNA Server 2.11 Service Pack 2
 * Microsoft SNA Server 3.0 Service Pack 4
 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 3.0 Service Pack 2

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This article was previously published under Q175321



SYMPTOMS
When connecting SNA Server to a host system over 802.2 through an IBM 3174 (though this does not require a 3174 to occur), all SNA clients suddenly stop receiving any responses to user requests. If 3270 emulation is being used, 3270 users may get stuck in a perpetual XCLOCK state and never receive a host response. This problem may also occur with TN3270 clients that connect through the SNA Server TN3270 server.



CAUSE
A portion of the problem was related to a previous Windows NT Dlc.sys problem. For additional information, please see the following article in the Microsoft Knowledge Base:

ARTICLE-ID: 168662

TITLE : DLC May Fail When Connecting Through an IBM 2210 Router



Windows NT 3.51
The Windows NT 3.51 fix should have the following time stamp:

Windows NT 4.0
To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

152734 How to Obtain the Latest Windows NT 4.0 Service Pack



STATUS
Microsoft has confirmed this to be a problem in Windows NT version 3.51. A supported fix is now available, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next service pack that contains this fix. Contact Microsoft Technical Support for more information.

Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.



MORE INFORMATION
This problem has been observed when using SNA Server on top of Windows NT 4.0 Service Pack 3 Dlc.sys driver, although it may occur with previous Windows NT 4.0 service pack levels and also with Windows NT 3.51. If the SNA Server is stopped and restarted, the 802.2 connection stays in a Pending state and does not reactivate. The only way to recover the 802.2 connection is to restart the server running both Windows NT and SNA Server.

SNA Server 802.2 link service Level 2 traces will show that the link service has several outstanding calls to the Windows NT Dlc.sys TRANSMIT.I.FRAME function that never complete. A network monitor LAN trace shows that Windows NT stops sending any DLC I-frames to the remote SNA system, although I-frames continue to be accepted from the remote system. The problem starts to occur after Windows NT DLC receives a REJ response to a retransmitted I-frame. The following network monitor trace illustrates the problem:

 Src Addr Dst Addr  Description ---

SNASRV   HOST      I DSAP=0x04 SSAP=0x04 C N(S) = 0x0B, N(R) = 0x10 SNASRV   HOST      I DSAP=0x04 SSAP=0x04 C N(S) = 0x0C, N(R) = 0x10 POLL HOST     SNASRV    RR DSAP=0x04 SSAP=0x05 R N(R) = 0x0B FINAL SNASRV   HOST      I DSAP=0x04 SSAP=0x04 C N(S) = 0x0B, N(R) = 0x10 POLL HOST     SNASRV    I DSAP=0x04 SSAP=0x04 C N(S) = 0x10, N(R) = 0x0B HOST     SNASRV    I DSAP=0x04 SSAP=0x04 C N(S) = 0x11, N(R) = 0x0B SNASRV   HOST      RR DSAP=0x04 SSAP=0x05 R N(R) = 0x11 HOST     SNASRV    I DSAP=0x04 SSAP=0x04 C N(S) = 0x12, N(R) = 0x0B HOST     SNASRV    RR DSAP=0x04 SSAP=0x05 R N(R) = 0x0C SNASRV   HOST      RR DSAP=0x04 SSAP=0x05 R N(R) = 0x13 HOST     SNASRV    RR DSAP=0x04 SSAP=0x05 R N(R) = 0x0D FINAL HOST     SNASRV    REJ DSAP=0x04 SSAP=0x05 R N(R) = 0x0D FINAL HOST     SNASRV    I DSAP=0x04 SSAP=0x04 C N(S) = 0x13, N(R) = 0x0D HOST     SNASRV    I DSAP=0x04 SSAP=0x04 C N(S) = 0x14, N(R) = 0x0D SNASRV   HOST      RR DSAP=0x04 SSAP=0x05 R N(R) = 0x15 HOST     SNASRV    I DSAP=0x04 SSAP=0x04 C N(S) = 0x15, N(R) = 0x0D SNASRV   HOST      RR DSAP=0x04 SSAP=0x05 R N(R) = 0x16 SNASRV   HOST      RR DSAP=0x04 SSAP=0x04 C N(R) = 0x16 POLL

In the above trace, Windows NT (SNASRV) sends I-frames 0x0B and 0x0C, setting the POLL bit after sending I-frame 0x0C. The host does not ack these I-frames, causing Windows NT (SNASRV) to resend I-frame 0x0B in line 4 above. The host eventually acks the I-frame 0x0C, but it then REJects the resend of I-frame 0x0B. After Windows NT DLC receives the host REJ (to the retransmitted I-frame 0x0B), Windows NT DLC never sends any more I-frames to the host. As this occurs, the SNA Server 802.2 link service's calls to TRANSMIT.I.FRAME stop responding (hang) and never complete.

Keywords: kbbug kbdriver kbfix kbinterop kbnetwork KB175321

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