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Revision as of 10:22, 10 August 2009 by Yan (Talk | contribs)

Windows registry settings

This page describes best practice for configuring Windows TCP\IP related parameters to archive the best performance with Windows guests. Those parameters are unrelated to kvm\VirtIO drivers , rather general Windows settings. After changing those setting reboot is required for the changes to effect the system.

Registry settings

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

"DefaultSendWindow"=dword:00100000

"DefaultReceiveWindow"=dword:00100000

"FastSendDatagramThreshold"=dword:00004000


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

"Tcp1323Opts"=dword:00000001

"TcpWindowSize"=dword:00100000


  • Tcp1323Opts - allows the scaling of the TCP window above 16k. For more info read Tcp1323Opts
  • "DefaultSendWindow", "DefaultReceiveWindow" and "TcpWindowSize" control TCP window size
  • "FastSendDatagramThreshold" - controls fast UDP transmit.

Additional links