I recently purchased a Windows Vista laptop and it worked great, well as soon as I bumped it to 2 gigs of RAM.   I was able to use the laptop at home and at one of my offices, both were on comcast cable.  I then took the laptop to the warehouse which was on Windstream DSL and to my surprise it would hardly cerf the net because my dsl was so slow.  No mater what page I went to some of the page would show up but it would never load an entire page.  I knew right then that it was most likely an MTU problem.  So I did some research and found that Vista tries to make guesses on what it should set your MTU settings for each connection to.  I disabled this and set my MTU manually to 1430 and walla everything worked like a champ.  Here is what I did…

1. You must get into a command prompt as Administrator.  To do this…

• Click Start and type cmd in the Search box. This should produce a list consisting of one entry: the shortcut to the Windows Command Processor, cmd.
• Right-click the cmd shortcut and choose Pin to Start Menu.
• Click Start again. Right-click the Command Prompt shortcut you just added to the Start menu and choose Properties.
• Click the Advanced button and click to select the Run as administrator check box.
• Click OK to save your changes.         

2. You must tell vista not to autotune itself and to abide by your MTU setting to do this at the cmd prompt type….

netsh int tcp set global autotuninglevel=disabled

3. And finally you must list set the MTU to each interface you want to change.  At the cmd prompt type….

netsh interface ipv4 set subinterface “Local Area Connection” mtu=1430 store=persistent

If you just want to see what your MTU settings are or find other interface names you can run….

netsh interface ipv4 show subinterfaces

Hope this Helps! 

Chris Edwards