Microsoft KB Archive/263088

= Windows 2000 Does Not Use Configured TCPWindowSize Registry Parameter When Accepting a Connection =

Article ID: 263088

Article Last Modified on 3/1/2007

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Professional Edition

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This article was previously published under Q263088



SYMPTOMS
Windows 2000 does not use the configured TCPWindowSize registry parameter when accepting a connection (SYN-ACKing) if you configure the parameter per interface and if the value is equal to or greater than 64240 (it uses a window size of 17520 instead, if you are using Ethernet).



CAUSE
The TCP connection accept functionality does not correctly parse the window size if you configure the parameter per interface.



RESOLUTION
To resolve this issue, set the TCPWindowSize value globally or use a value smaller than 64240 (this value is a multiple of the Ethernet Maximum Segment Size).



STATUS
Microsoft has confirmed this to be a problem in Microsoft Windows 2000.



MORE INFORMATION
The TCPWindowSize registry parameter determines the maximum TCP receive window size offered by a computer when establishing a TCP connection. The receive window specifies the number of bytes that a sender can transmit without receiving an acknowledgment.

You can set the TCPWindowSize parameter in either of the following locations in the registry in Windows 2000:

Global:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tcpip\Parameters

Per interface:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\

Although the TCP window size used by the Internet Protocol (IP) stack may not be the same value configured using the TCPWindowSize registry parameter, the value should be obtained by rounding up the TCPWindowSize to a multiple of the Ethernet Maximum Segment Size (MSS), which is 1460 for Ethernet. To use a TCP window size greater than 65535, you need to turn on the Window Scaling option.

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

172983 Explanation of the Three-Way Handshake via TCP/IP

224829 Description of Windows 2000 TCP Features

Keywords: kbbug kbnofix kbenv kbstack KB263088

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