DOCUMENT:Q166222 09-AUG-2001 [winnt] TITLE :Dlc.sys Sends Frame Reject (FRMR) and Drops Connection PRODUCT :Microsoft Windows NT PROD/VER:winnt:3.51 (all service packs),4.0,4.0 SP1,4.0 SP2,4.0 SP3,4.0 SP4,4.0 SP5,4.0 SP6,4.0 OPER/SYS: KEYWORDS:kbnetwork kbAPI kbDLC kbSDKPlatform kbGrpDSNet ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Server versions 3.51 (all service packs), 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4, 4.0 SP5, 4.0 SP6, 4.0 SP6a - Microsoft Windows NT Workstation versions 3.51 (all service packs), 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4, 4.0 SP5, 4.0 SP6, 4.0 SP6a ------------------------------------------------------------------------------- SYMPTOMS ======== On Windows NT, when you run an application that uses Dlc.sys to communicate to a remote system using DLC/802.2 over Token Ring, Ethernet, or FDDI, Windows NT may erroneously send a frame reject (FRMR) and drop the connection. If SNA Server is being used, this will cause an SNA Server connection failure with the following Windows NT application event log entries: Event 228: SNA Server FRMR sent (0x03) = invalid or unsupported command/response received Event 238: SNA Server Connection statistics Event 23, SNA Server Connection using Link Service failed Qualifier = 00AC When this occurs, all SNA sessions using this connection will be lost. The following excerpt from a network monitor trace illustrates the reproduction scenario: Frame Src MAC Dst MAC Description 1 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x07, N(R) = 0x1A 2 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x08, N(R) = 0x1A 3 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x09, N(R) = 0x1A 4 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x0A, N(R) = 0x1A 5 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x0B, N(R) = 0x1A 6 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x0C, N(R) = 0x1A 7 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x0D, N(R) = 0x1A 8 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x0E, N(R) = 0x1B POLL 9 HOST SNASRV RR DSAP=0x04 SSAP=0x05 R N(R) = 0x07 FINAL 10 SNASRV HOST I DSAP=0x04 SSAP=0x04 C N(S) = 0x07, N(R) = 0x1B POLL 11 HOST SNASRV I DSAP=0x04 SSAP=0x04 C N(S) = 0x1B, N(R) = 0x07 12 HOST SNASRV RR DSAP=0x04 SSAP=0x05 R N(R) = 0x08 13 HOST SNASRV RR DSAP=0x04 SSAP=0x05 R N(R) = 0x09 14 SNASRV HOST FRMR DSAP=0x04 SSAP=0x05 R CAUSE ===== Windows NT Dlc.sys was incorrectly handling acknowledgements for I-frames when the t1 send timer has expired on a DLC connection. In the above trace of LLC frames, SNA Server sends a window of I-frames to the host from frame 1-8, with the N(S) counter incremented from 0x07-0x0E. The host then replies with a N(R) of 0x07, causing SNA Server to reset its N(S) counter and begin resending the I-frames again. However, SNA Server then receives host acknowledgments for later frames (sending N(R) = 0x08 and 0x09 in frame 12 and 13 above). Because the Windows NT DLC driver detects that the N(S) is now 0x07, DLC sends a frame reject (FRMR) to the host, causing the connection to drop. RESOLUTION ========== It is possible to work around this problem by increasing the DLC t1 timer so that it will never expire. If SNA Server is being used, the t1 timer can be increased to a maximum value of 10 within the connection properties dialog or folder within SNA Server 2.x Admin or SNA Server 3.x Manager. An update to Dlc.sys is available to correct this problem. The Dlc.sys driver now keeps track of a new maximum N(S) counter sent value and validates I-frame acknowledgements based on this value STATUS ====== Microsoft has confirmed this to be a problem in Windows NT version 3.51 (SP1-SP5) and Windows NT 4.0 (SP1, SP2). This problem was corrected in the latest Microsoft Windows NT 4.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces): S E R V P A C K Additional query words: 2.0 2.1 2.11 3.0 4.00 3.51 prodnt ====================================================================== Keywords : kbnetwork kbAPI kbDLC kbSDKPlatform kbGrpDSNet Technology : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT400search kbWinNTW351search kbWinNTW351 kbWinNTW400sp5 kbWinNTW400sp4 kbWinNTW400sp3 kbWinNTW400sp2 kbWinNTW400sp1 kbWinNTSsearch kbWinNTS400sp6 kbWinNTS400sp5 kbWinNTS400sp4 kbWinNTS400sp3 kbWinNTS400sp2 kbWinNTS400sp1 kbWinNTS400search kbWinNTS400 kbWinNTW400sp6 kbWinNTW400SP6a Version : winnt:3.51 (all service packs),4.0,4.0 SP1,4.0 SP2,4.0 SP3,4.0 SP4,4.0 SP5,4.0 SP6,4.0 SP6a ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. 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