Interpreting 802.2 DLC Outage Code from SNA Server Level 2 Trace
ID: Q170777
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The information in this article applies to:
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Microsoft SNA Server, versions 2.0, 2.1, 2.11, 3.0
SUMMARY
The SNA Server 802.2 DLC link service communicates over the Windows NT
DLC transport protocol to support DLC connections over Token Ring,
Ethernet, or FDDI. If a 802.2 DLC connection is lost for any reason,
the Windows NT DLC interface returns a DLC status code in a DLC READ
response to the SNA Server 802.2 link service. This status code is
interpreted by the link service and mapped to the actual "qualifier"
that is reported in the Windows NT application event log as follows:
Source: SNA Server
Event ID: 23
Description:
Connection <name> using Link Service <link> failed.
Qualifier = 00xx
The qualifier codes are documented in the SNA Server Reference Guide.
For 802.2 links, the following qualifiers can occur:
29 = Remote node not active
AE = DISC/DM received
AF = Link lost
AB = SABME received while connection active
AC = FRMR (frame reject) sent
AD = FRMR (frame reject) received
If a FRMR is causing the connection failure, SNA Server will indicate
additional information about the FRMR in one of the following events:
Event 227 FRMR received
(Windows NT DLC received a FRMR from the remote system)
Event 228 FRMR sent
(Windows NT DLC sent a FRMR to the remote system)
These events include a "FRMR code" returned by DLC to indicate the cause
of the FRMR.
This article describes how to interpret the DLC status code returned
by the DLC READ response, which can be captured within an SNA Server
802.2 link service "Level 2" trace.
NOTE: It is not necessary to decode the READ response from a Level 2
trace to determine the cause of a failure, since the Event 23, 227, and
228 events already indicate the relevant information.
MORE INFORMATION
The Windows NT DLC programming interface (DLCAPI.DLL), supports the
CCB2 DLC interface, as documented by the IBM Local Area Network
Technical Reference (IBM document #SC30-3383). This interface is
used by the SNA Server 802.2 link service to support SNA communication
over Token Ring, Ethernet, and FDDI.
After an 802.2 DLC connection is established, the DLC interface
indicates a connection failure to SNA Server by responding to a
DLC READ command and indicating a DLC Status code. Here is the
format of the READ structure returned by DLC:
CCB2 Structure
==============
Parameter Byte Len Type Description
CCB_ADAPTER 1 DB Adapter number (0 or 1)
CCB_COMMAND 1 DB Command field (31 = READ)
CCB_RETCODE 1 DB Completion code
CCB_WORK 1 DB Adapter support software work area
CCB_POINTER 4 DW Queue pointer
CCB_CMPL_FLAG 4 DD Command completion flag
CCB_PARM_OFFSET 2 DW Offset to CCB2 parameter table
(Pointer to READ Parameter Table below)
[ other parameters ]
CCB2 Parameter Table for READ
=============================
Parameter Byte Len Type Description
STATION_ID 2 DW SAP station ID
OPTION_INDICATOR 1 DB READ option indicator
EVENT_SET 1 DB Set of events for notification
EVENT 1 DB Posting event (*)
CRITICAL_SUBSET 1 DB Critical event subset identifier (*)
<reserved> 2 DB <unused > (**)
NOTIFICATION_FLAG 4 DD Event user notification flag (*)
STATION_ID 2 DW Station ID
DLC_STATUS_CODE 2 DW DLC status code
FRMR_DATA 5 DB Five byte FRMR "reason code"
ACCESS_PRIORITY 1 DB New access priority if status bit 5 is "on".
REMOTE_NODE 6 DB 6-byte remote node address
REMOTE_SAP 1 DB Remote SAP address
<reserved> 1 DB <unused>
USER_STAT_VALUE 2 DW User value as defined in DLC.OPEN.SAP command
(*) Indicates a returned value
(**) In Windows NT DLC, there are 2 unused bytes resulting from the
use of a non-packed CCB2 structure
Using the SNA Server Trace program (SNATRACE), it is possible to capture
all DLC calls made by the 802.2 link service to the Windows NT DLC
interface by enabling "Level 2" message tracing. If a DLC connection
failure occurs, a DLC READ command will complete, and may appear as
follows:
DLC --------------------------------------------------
DLC READ OK
DLC ---- DLC API control block at address 7c5e0----
DLC 00310000 00000000 00000000 FCC50700
DLC D4000000 00000000 00002000
DLC
DLC 0004010C 08000000 01000000 01040040
DLC 00000000 00004201 02998122 04041FC0
DLC --------------------------------------------------
The first two lines correspond to the CCB2 structure passed in the
DLC API control block, while the last two lines correspond to the
CCB parameter table for the READ command. Using the structure definition
above, the parameter table can be interpreted as follows:
0004 = station ID
01 = option indicator
0C = event set
08 = event
00 = critical subset
0000 = padding (unused)
01000000 = notification flag
0104 = station ID (non-Intel format = 0401)
0040 = DLC status code (non-Intel format = 4000)
00000000 00 = FRMR data
00 = access priority
42 01 02 99 81 22 04 = remote node address
04 = remote SAP
1F = reserved
C0 = user status value
Note that the DLC status code (DW = two byte "word" value) is stored in
memory in Intel format, and needs to be "flipped" to show the real value
as interpreted by the 802.2 link service.
Using the DLC status code definitions below (as documented in Appendix B
of the IBM LAN Technical Reference), a status code of 0x4000 is interpreted
as follows:
0x4000 (hex) = 0100 0000 0000 0000 (binary)
Bit 14 on = DM or DISC received
DLC Status Codes
=================
BIT Function
15 Link lost
14 DM or DISC received
13 FRMR received (See 5-byte FRMR data "reason code")
12 FRMR sent (See 5-byte FRMR data "reason code")
11 SABME received for an open link station
10 SABME received, link station opened
9 Remote station has entered "local busy" condition
8 Remote station has left a "local busy" condition
7 Ti has expired
6 DLC counter overflow (DLC.STATISTICS should be called)
5 Access priority lowered
4-1 reserved
0 Local station has entered a "local busy" condition
Additional query words:
Keywords : prodsna snadlc
Version : WINDOWS:2.0,2.1,2.11,3.0
Platform : WINDOWS
Issue type : kbhowto