Q97491: Duplicate LOGON Names Can Disrupt Messenger Service

Article: Q97491
Product(s): Microsoft LAN Manager
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 30-JUL-2001

SUMMARY
=======

Duplicate names registered to the messenger service cause the lengthy error
message shown below. The process by which duplicate names can occur and
suggestions for avoiding the problem are discussed after the message.

LAN Man 2.1a, Token Ring, NetBEUI

Sample from LM Error Log:

  

  MESSENGER      3106     01-25-93 05:47pm
  NET3106: An unexpected NCB was received. The NCB is the data.
  91 19 3F 08 58 05 27 01 C8 00 2A 20 20 20 20 20   ..?.X.'...*
  20 20 20 20 20 20 20 20 20 20 41 44 4D 49 4E 20
  ADMIN
  20 20 20 20 20 20 20 20 20 03 3C 28 28 00 02 00
  .<((...
  00 19 00 00 00 00 00 00 00 00 00 00 31 03 00 00
  ............1...

  MESSENGER      3106     01-25-93 05:47pm
  NET3106: An unexpected NCB was received. The NCB is the data.
  92 02 3F 08 58 05 27 01 C8 00 2A 20 20 20 20 20   ..?.X.'...*
  20 20 20 20 20 20 20 20 20 20 41 44 4D 49 4E 20
  ADMIN
  20 20 20 20 20 20 20 20 20 03 3C 28 28 00 02 00
  .<((...
  00 08 00 00 00 00 00 00 00 00 00 00 31 03 00 00
  ............1...

  (1st error)
  Byte 1:(NCB CMD)   91 = NCB Listen
  Byte 2:(RET CODE)  19 = Name Conflict

  (2nd error)
  Byte 1:  92 = NCB Hangup
  Byte 2:  08 = Illegal local session Number

MORE INFORMATION
================

This is caused by two machines starting up with the same "unique" name. Although
this shouldn't happen, there are certain unusual conditions when it can and
does.

In this example, the Admin logs in on one machine, replacing the machine name as
the primary NetBIOS name and making the original machine name secondary.
Sometime later, ADMIN logs in on the second server. When the standard login
broadcast goes out to see if there is another system entity logged on as ADMIN,
the first machine doesn't answer for some reason--maybe it has been disconnected
momentarily or is using a slow link and doesn't respond in time. The second
ADMIN thus is configured as the only ADMIN in the system, so it supersedes the
machine name as the primary NetBIOS name just as the first ADMIN did on its
machine. Now two machines have ADMIN as their primary NetBIOS name and when
alerts go out to user ADMIN, messenger generates the long message above
reporting a duplicate name on the net.

If all the machines could "see" each other all the time, the first Admin to log
on would be known as Admin and subsequent Admins would use their machine names.
This would ensure unique NetBIOS names and alleviate the problem. But system
characteristics such as slow links keep machines from being in constant contact
and problems such as this one, though rare, can occur.

To fix this, make sure your remote links are always there and up to standards. If
you logon Admin at several machines in your system, get a different Admin login
name for each server.

Additional query words: 2.00 2.10 2.10a 2.20

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