Windows Vista & 7 - Very slow RDP connection to Win2003 64 bit server

Microsoft Remote Desktop Client 6.0 which comes pre-installed with Vista (and Win 7) is very slow when you try connecting to some Windows 2003 servers. In particular, Windows 2003 R2 64-bit Server. Here is what you need to do to resolve this issue:

Apparently this problem is because Windows Vista has a low initial setting on it’s Auto Tuning feature. What Auto-Tuning does is continually adjusts the TCP/IP receive windows size based on current (and changing) network conditions. It seems that many people have reported problems with auto-tuning causing various network timeout issues with some applications and routers.
If you’re experiencing any of these problems, a supported hotfix is available from Microsoft. See KB947773 at Microsoft Support website for more info and download information.

Workaround
Use one of the following workarounds, as appropriate for your situation. You can turn off Auto Tuning as described below.

 - Run a command prompt (cmd.exe) as an Administrator (must have administrator privileges)
Type:

netsh interface tcp set global autotuninglevel=disabled

Disable the autotunning feature in Vista completely, and fit and lock the RWIN receive window to default value 65536 bytes.

If you want to to re-enable it, type:

netsh interface tcp set global autotuninglevel=normal

In some cases you may need to use this command in addition to the above:

netsh interface tcp set global rss=disabled

Update! This command makes your network connection EVEN FASTER:

netsh interface tcp set global autotuninglevel=highlyrestricted

And if you’d like to just view the states of your current TCP parameters, you can use this command:

netsh interface tcp show global

Resources:

This Microsoft Fix it disables TCP auto-tuning and is available in the following Knowledge Base articles:
932170
934430
935400
947239
947773
951291