Random Blue Screens Caused by Bad Packet and DLC.SYS

 Last reviewed: March 24, 1997
Article ID: Q152304
The information in this article applies to:
  • Microsoft Windows NT Workstation versions 3.51
  • Microsoft Windows NT Server versions 3.51

SYMPTOMS

A Windows NT STOP Message (Blue Screen), frequently a BugCheck 0x0000000A, is displayed due to a corrupt Ethernet 802.3 packet received by DLC.SYS.

CAUSE

An assumption was made by DLC.SYS that a Length Field (LPDU Length) in the 802.3 Ethernet header was valid. This length field should always be 3 or greater.

An IEEE 802.3 Frame has the following format. 

|<------------------ Maximum Length 1532 Bytes ------------------>|
V                                                                 V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-//--+-+-+-+-+-+-+-+ 
|  PREAMBLE   |S| DEST ADDR | SRC ADDR  |LP | LPDU  |Pad  |  FCS  |
|  7 Bytes    |D|  6 Bytes  |  6 Bytes  |DU | Bytes |     |4 Bytes|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-//--+-+-+-+-+-+-+-+ 
                                                |
                                                |
                                 /--------------/
      |                          |                        |
      V                          V                        V
    <-+--------+--------+--------+--------+-------//------+>
      |  DSAP  |  SSAP  |  Control Field  | Information   |
      | 1 Byte | 1 Byte |  1 or 2 Bytes   |  Field        |
    <-+--------+--------+--------+--------+-------//------+>

                     IEEE 802.3 Frame Format
The field lengths are as follows: 

     * Preamble - 7 bytes
     * Start Delimiter (SD) - 1 byte
     * Destination Address (DEST ADDR)- 6 bytes
     * Source Address (SRC ADDR) - 6 bytes
     * LPDU Length (Length of the LLC Protocol Data Unit) - 2 bytes
       (This field should always have a value of 3-1500)
     * LPDU (LLC Protocol Data Unit) - variable length (3-1500 bytes)
       - Destination SAP Address (DSAP) - 1 byte
       - Source SAP Address (SSAP) - 1 byte
       - Control Field - 1 or 2 bytes
       - Informational Field - variable length (0-1497)
     * Pad - 0 to 43 bytes
     * Frame Check Sequence (FCS) - 4 bytes
In the case that caused the Windows NT STOP Message, a corrupt IEEE 802.3 frame was received by DLC.SYS with a LPDU Length field of 0 (which is invalid). Because every LLC Protocol Data Unit (LPDU) consists of a 1 byte DSAP, 1 byte SSAP, and at least a 1 byte Control Field, the LPDU Length should always be at least 3.

RESOLUTION

A change was made to DLC.SYS to inspect the LPDU Length field and to discard all IEEE 802.3 packets whose length fields are invalid (less than 3).

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 3.51. This problem was corrected in the latest Windows NT 3.51 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: prodnt Instability Pool Memory Corruption
Keywords : kbbug3.51 kbnetwork ntnetserv ntprotocol NTSrvWkst ntstop
Version : 3.51
Platform : WinNT

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Last reviewed: March 24, 1997
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