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Q221926: TCP/IP Forwarding Buffer Grows to Use Available Kernel Memory

Article: Q221926
Product(s): Microsoft Windows NT
Version(s): winnt:4.0 SP4
Operating System(s): 
Keyword(s): 
Last Modified: 11-JUN-2002

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0 SP4 
- Microsoft Windows NT Workstation version 4.0 SP4 
- Microsoft Windows NT Server, Enterprise Edition version 4.0 SP4 
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IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

  Q256986 Description of the Microsoft Windows Registry

SYMPTOMS
========

The forward buffer used with TCP/IP to buffer routed packets between interfaces
can grow to use all available kernel memory in Windows NT computers running
Windows NT 4.0 Service Pack 4.

Or, you may see the following event information in the System log in Event
Viewer:

  Event ID: 2019
  Description: The server was unable to allocate from the system nonpaged pool
  because the pool was empty.

CAUSE
=====

The default maximum forwarding buffer size is 0xFFFFFFF bytes. Therefore, the
buffer can grow to use all available system resources in this configuration.

RESOLUTION
==========

WARNING: If you use Registry Editor incorrectly, you may cause serious problems
that may require you to reinstall your operating system. Microsoft cannot
guarantee that you can solve problems that result from using Registry Editor
incorrectly. Use Registry Editor at your own risk.

To work around this problem, add the following registry entries to the server
running Windows NT 4.0 and modify the values to disallow memory usage to degrade
system performance:

  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

- MaxForwardBufferMemory (REG_DWORD: 74240)

  Establishes the maximum number of bytes of memory that the IP can allocate to
  store packet data in the router packet queue. This value must be greater than
  or equal to the value of ForwardBufferMemory.

  This registry entry is a decimal value.

- MaxNumForwardPackets (REG_DWORD: 50)

  Establishes the maximum number of IP packet headers that can be allocated to
  the router packet queue. This value must be greater than or equal to the
  value of NumForwardPackets.

  This registry entry is a decimal value.

These values can be modified in accordance with the instructions to allocate more
resources for the forwarding buffer, but increasing them excessively will have a
negative effect on other system resources.

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT version 4.0.


Additional query words: TCPu UPCT poolmon

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Keywords          :  
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400search kbWinNT400search kbWinNTW400sp4 kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400sp4 kbWinNTS400sp4 kbWinNTS400search
Version           : winnt:4.0 SP4
Issue type        : kbbug
Solution Type     : kbnofix

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