Sometimes it is helpful to disable Windows Vista's autotuning of TCP/IP.

Some networking devices, such as SPI firewalls, some NAT routers, VPN endpoints, WiFi devices have problems with the way Windows Vista resizes the TCP Window. Possible symptomps include: web traffic ok, email timeouts on receiving only, slow or no network file server access, random network timeouts or connectivity problems, freezing or slow web browsing or VPN connections.

Note that disabling TCP Window autotunning limits the TCP Window to 65535, which may not be adequate for faster broadband internet connections.

To disable TCP/IP autotunning, in "Elevated" Command Prompt type:

netsh interface tcp set global autotuning=disabled

To verify that it is dsabled:

netsh interface tcp show global

To set back to the default Windows Vista behavior:

netsh interface tcp set global autotuningl=normal


Note: To get elevated command prompt (admin priviledges), you may need to do the following:
- Click the Start button
- In the Search box, type: Command Prompt
- Right-click on the Command Prompt icon and select "Run as administrator"


Note: You can also change the default auto-tunning behavior in other ways, for example typing this in command prompt: netsh int tcp set global autotuninglevel=highlyrestricted
The above command helps with servers that do not fully support RFC 1323. See: MSKB929868


See also:
Windows Vista Elevated Command Prompt
Windows Vista Tweaks