Microsoft KB Archive/221926

= TCP/IP Forwarding Buffer Grows to Use All Available Kernel Memory =

Article ID: 221926

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT 4.0 Service Pack 4
 * Microsoft Windows NT Workstation 4.0 Developer Edition
 * Microsoft Windows NT 4.0 Service Pack 4

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This article was previously published under Q221926



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:

256986 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 that this is a problem in Windows NT version 4.0.

Additional query words: TCPu UPCT poolmon

Keywords: kbbug kbnofix KB221926

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