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Q297040: Windows May Hang When Attempting to Establish a TCP Connection

Article: Q297040
Product(s): Microsoft Windows NT
Version(s): 4.0,4.0 SP6,4.0 SP6a
Operating System(s): 
Keyword(s): 
Last Modified: 08-MAY-2002

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The information in this article applies to:

- Microsoft Windows NT Server versions 4.0, 4.0 SP6a 
- Microsoft Windows NT Server versions 4.0, 4.0 SP6, Terminal Server Edition 
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SYMPTOMS
========

A Windows NT 4.0-based server with a recent post-SP6a hotfix, or a Windows NT
4.0 Terminal Server with a recent post-SP6 hotfix, may stop responding (hang) if
it attempts to make a TCP connection with an IP address that is nonexistent.

For example, if a Windows NT 4.0-based server with an address of 129.68.72.10
attempts to connect by using Telnet to an address of 129.68.72.40, and that
address is either nonexistent or unavailable, the server may hang. This is a
"hard" hang with no mouse control and no CTRL+ALT+DELETE functionality
available. The server is unresponsive from the console and cannot be pinged on
the network.

For this hang to occur, the TCP/IP SynAttackProtect registry value must be set.
For additional information about this registry entry, click the article number
below to view the article in the Microsoft Knowledge Base:

  Q142641 Internet Server Unavailable Because of Malicious SYN Attacks

CAUSE
=====

Under certain circumstances, the spinlock for the TCP/IP connection table lock
is acquired but not released; this causes the server to hang.


RESOLUTION
==========

A supported fix is now available from Microsoft, but it is only intended to
correct the problem described in this article and should be applied only to
systems experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the
fix. For a complete list of Microsoft Product Support Services phone numbers and
information on support costs, please go to the following address on the World
Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are normally incurred for support calls may
be canceled, if a Microsoft Support Professional determines that a specific
update will resolve your problem. Normal support costs will apply to additional
support questions and issues that do not qualify for the specific update in
question.

The English version of this fix should have the following file attributes or
later:

  Date         Time   Size     File name
  --------------------------------------
  27-Apr-2001  15:54  174,896  Tcpip.sys

NOTE: Because of file dependencies, this hotfix requires Microsoft Windows NT 4.0
Service Pack 6a.



STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products that are
listed at the beginning of this article.

Additional query words: freeze lock lockup

======================================================================
Keywords          :  
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400sp6 kbWinNTS400search kbWinNTS400 kbNTTermServ400 kbNTTermServ400sp6 kbNTTermServSearch
Version           : :4.0,4.0 SP6,4.0 SP6a
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

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