Netbios Delays Sending/Receiving Packets When Session Is Lost

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On a network running NetBIOS over TCP/IP, you may notice that, if a client's connection to a Windows NT server fails or experiences a loss of session, this causes delays in sending or receiving data from other clients to and from the server.


During a failed or disconnected client session to the server, you may notice, using Network Monitor, that you can see the server is receiving packets from the other clients; however, NetBIOS is not passing packets back up to the clients. This will also show that all the send buffers have been consumed and they are waiting for the server to respond (this is with a low level NetBIOS ACK, not a NetBIOS packet). The Network Monitor trace shows that TCP/IP has already ACK'd these packets but the NetBIOS layer has not.

It will appear that the NetBIOS layer is blocked, waiting for something just after the lower level protocol has notified it of a session failure.

NOTE: The problem does not occur until TCP/IP sees that there is a timeout.

When in this state, the NetBIOS interface will not process any command. Even simple commands like Adapter Status will be blocked. You may pass any NO_WAIT commands to NetBIOS; however, these will not be processed until it recovers.


To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
152734 How to Obtain the Latest Windows NT 4.0 Service Pack


Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.


Article ID: 186873 - Last Review: October 8, 2013 - Revision: 2.2
  • Microsoft Windows NT Server 4.0, Terminal Server Edition
  • Microsoft Windows NT Server 4.0 Standard Edition
kbnosurvey kbarchive kbhotfixserver kbqfe kbbug kbfix KB186873

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