How to enable and configure Windows 2003 TCPIP Windows Scaling

Author: NetworkAdminKB.com
Created: 2003-02-13
Modified: 2011-02-25

Information:

To enable TCPIP Windows Scaling on Windows 2003 Server the TcpWindowSize must be greater than 64k (65536) and you must configure the Tcp1323Opts=1 to force the Window 2003 Server to always use TCPIP Window Scaling.  Finally, you should enable Selective Acknowledgements to properly enable TCPIP Window Scaling.  This should be done on both the source and target servers to be maximize the effectiveness of this setting.

 

Also, there is an issue with TCPIP Window Scaling configuration when both computers are not configured or do not to support TCPIP Window Scaling.  In that case only the yyyy octets below are used to create the normal TCPIP Window Size.  Therefore, to provide the most flexible implementation of Window Scaling it is advisable to view the DWORD for this setting as 2 parts.

 

"TcpWindowSize"=dword:xxxxyyyy

xxxx = The scaling (multipling) number

yyyy = The actual size of the TCP Window

Therefore, setting "TcpWindowSize"=dword:0003FAF0 would result in a packet capture as follows.

 

    + TCP: Flags = 0x02 : ....S.

     TCP: Window = 64240 (0xFAF0)

      TCP: Checksum = 0x4A72

      TCP: Urgent Pointer = 0 (0x0)

      TCP: Options

        + TCP: Max Segment Size

          TCP: Option Nop = 1 (0x1)

        - TCP: Window Scale Option

              TCP: Option Type = 3 (0x3)

              TCP: Option Length = 3 (0x3)

             TCP: Window Scale = 3 (0x3)

 

 

Save the following as a registry file, configure the TcpWindowSize settings as desired and run on the desired computers, then reboot.

 

Windows Registry Editor Version 5.00

 

;Tcp1323Opts must be set to 1 or 3 per RFC 1323

;Values for Tcp12Opts

;0 (disable RFC 1323 options)

;1 (window scale enabled only)

;2 (timestamps enabled only)

;3 (both options enabled)

 

;The Default for Tcp1323Opts is "No Value" meaning that the entry does not exist and therefore Window 2003 Server behaves as follows: Do not initiate options but if requested provide them.

 

;This means that when initiating file transfers from the server Windows Scaling is not provided by

;Default.  You must FORCE ENBLE IT.

 

;Finally if Windows Scaling is Enabled the Selective Acknowledgements should be also.

;SackOpts = 1 to enable (default), 0 to disable

 

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]

"TcpWindowSize"=dword:0003FAF0

"Tcp1323Opts"=dword:00000001

"SackOpts"=dword:00000001

 

More Information:

Description of Windows 2000 and Windows Server 2003 TCP Features

Appendix A: TCP/IP Configuration Parameters

 

Article ID: 310, Created On: 9/19/2011, Modified: 9/19/2011