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Microsoft KB Archive/100453

From BetaArchive Wiki

Article ID: 100453

Article Last Modified on 9/30/2003


  • Microsoft LAN Manager 2.2 Standard Edition

This article was previously published under Q100453


Connecting workstations and servers using different drivers can cause problems when using Source Level Routing across bridges using IBM PC- NET/TOKEN RING Bridge Program 1.01.

From     Topology     Driver     To     Topology     Driver     Successful?
PC     Token Ring     MS       Server   Token Ring     MS       Yes
PC     Token Ring     MS       Server   PC-NET         MS       No
PC     Token Ring     IBM      Server   Token Ring     MS       Yes
PC     Token Ring     IBM      Server   PC-NET         MS       No
PC     PC-NET         MS       Server   PC-NET         MS       Yes
PC     PC-NET         MS       Server   Token Ring     MS       No
PC     PC-NET         IBM      Server   Token Ring     MS       Yes
PC     PC-NET         IBM      Server   PC-NET         MS       No


NOT Supported by Microsoft

  • NetBEUI source routing on any topology except token ring
  • Source Level Routing on PC-NET cards under LAN Manager

Supported by Microsoft

  • use of IBM PC-NET cards as an 802.3 network


IBM PC-NET refers to a complete network involving PC NET drivers over PC-NET cards. Using LAN Manager on PC-NET cards is an Ethernet 802.3 network.


The LAN Manager PC-NET (802.3) mac layer does not understand the IBM PC-NET mac frame format, which includes a 2-byte field of all zeroes before the routing field. The IBM implementation of PC-NET uses this field, and adds a source routing information field, as shown below. Following the IEEE 802.3 implementation, Microsoft uses this field to indicate the length of the info field or type (dix), so a string of zeros is meaningless and the frame is disregarded. Also, the Microsoft 802.3 implementation does not include the Route Information field.

However, the token ring frames see the source routing field on both sides, IBM PC-NET and LAN Manager, because of the 802.5 frame definition:

802.3                             IBM          Microsoft

Start Delimiter                  1 Byte          1 Byte
Destination ID                   6 Bytes         6 Bytes
Source Address                   6 Bytes         6 Bytes
ZERO(IBM)/Length Count(MS)       2 Bytes         2 Bytes
Routing Information (IBM)        0-18 Bytes
Data/Information Field           Variable        Variable
Frame Check Sequence             4 Bytes         4 Bytes
Frame Status                     1 Byte          1 Byte
Pad                              Variable        Variable

To enable collision detection, the frame must contain at least 64 bytes, not including the Start Delimiter(SD) field. The combination of data and pad fields must be at least 46 bytes.

The Frame Check Sequence(FCS) field stores the CRC check from the sending side. When the receiving station performs its CRC, the results do not match, because of the zeros in the IBM ZERO field.

Additional query words: source routing PC-NET 2.20 2.2 pcnet pc net

Keywords: KB100453