Duplicate LOGON Names Can Disrupt Messenger Service (97491)

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.