DOCUMENT:Q165005
TITLE   :Windows NT Slows Down Due to Land Attack
PRODUCT :Microsoft Windows NT
PROD/VER:3.51 4.00
OPER/SYS:WINDOWS
KEYWORDS:kbbug kbbug3.51 kbbug4.00 kbenv kbfix3.51 kbfix4.00 kbpatch NTSrvWkst nttcp

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The information in this article applies to:

 - Microsoft Windows NT Workstation versions 3.51 and 4.0
 - Microsoft Windows NT Server versions 3.51 and 4.0
 - Microsoft Windows NT Server Enterprise Edition version 4.0
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SYMPTOMS
========

After receiving spoofed connection request (SYN) packets, Windows NT may
begin to operate slowly. After about one minute, Windows NT returns to
normal operation.

NOTE: This problem may occur with TCP/IP on other operating systems as
well.

CAUSE
=====

This behavior occurs due to "Land Attack". Land Attack sends SYN packets
with the same source and destination IP addresses and the same source and
destination ports to a host computer. This makes it appear as if the host
computer sent the packet to itself. Windows NT operates more slowly while
the host computer tries to respond to itself.

RESOLUTION
==========

Windows NT 4.0
--------------

To resolve this problem in Windows NT 4.0, obtain the following fix or wait
for the next Windows NT service pack.

This fix should have the following time stamp:

   11/25/97  04:54p        143,472 Tcpip.sys (Intel)
   11/25/97  04:52p        263,375 Tcpip.sys (Alpha)

This hotfix has been posted to the following Internet location:

   ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/
   hotfixes-postSP3/land-fix/

NOTE: The above link is one path; it has been wrapped for readability.

NOTE: This fix supercedes the ICMP-fix and the OOB-fix hotfixes.

Windows NT 3.51
---------------

To resolve this problem in Windows NT 4.0, obtain the following fix or wait
for the next Windows NT service pack.

This fix should have the following time stamp:

   12/02/97  02:24p               123,792 Tcpip.sys (Intel)
   12/02/97  02:21p               216,848 Tcpip.sys (Alpha)

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT versions 3.51 and 4.0.
A supported fix is now available, but has not been fully regression-tested
and should be applied only to systems experiencing this specific problem.
Unless you are severely impacted by this specific problem, Microsoft
recommends that you wait for the next Service Pack that contains this fix.
Contact Microsoft Technical Support for more information.

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

For information on the hotfix for Windows 95, please see the following
article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q177539
   TITLE     : Windows 95 Stops Responding Because of Land Attack

Additional query words: 3.51 4.00 port 139

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