Performance for virtual machines can be improved through many changes. An often overlooked consideration is networking.

Network slowdown can occur if your router doesn’t support TCP Window Scaling. This is easy to check.

1) You will need a command window with administrative access. Either through logon privilege or starting it with administrative access.

Netsh is a command-line scripting utility which will allow you to modify the network configuration while it’s running. This will help you decide if sliding window is in use.

2) Enter: netsh interface tcp show global






Look at Receive Window Auto-Tuning Level. This value can be changed. There are a few options. If you don’t know what to use, start with disabled. You can change this later on. There are five choices in all:

  • disabled – Set the receive window to default.
  • highlyrestricted – Set the receive window to grow beyond default but only for certain issues.
  • restricted – Set the receive window to grow even more.
  • normal – Set the receive window to grow at most scenerios
  • experimental – Set the receive window to grow for extreme scenerios.

3) Enter: netsh interface tcp set global autotuninglevel=disabled

4) Reboot the VM and see if it improves.  If not try a new setting.