Do you have a problem with certain websites loading verrrry sloooowly? Google around a bit and you’ll find you’re not the only one. Microsoft’s new network stack has had a number of different problems, most of them caused by the rest of the world not being completely up-to-date with the latest standards (backwards compatibility, who needs it!). This problem is no exception.
A recent Microsoft Knowledgebase article describes one potential cause of the problem: RFC 1323 compliance. Though the text suggests that it just affects the Enterprise version, the Applies To section lists all versions of Vista. In a nutshell, websites that don’t fully support RFC 1323 or the default Windows Scaling factor of 8 will be very slow or even unaccessible.
There is a workaround. Press the and type
cmd, then press CTRL+SHIFT+ENTER to open a command prompt as an administrator. At the command prompt, type:
netsh interface tcp set global autotuninglevel=highlyrestricted
This will set the autotuninglevel to “Allow the receive window to grow beyond its default value, but do so very conservatively.” If you want to put it back to the default setting, type:
netsh interface tcp set global autotuninglevel=normal
Note that another possible setting, mentioned in my post about slow threaded network downloads disables autotuning all-together with this command:
netsh int tcp set global autotuninglevel=disable
If this change doesn’t help, you should check for updates to your routers firmware (you should do this anyway) and if there isn’t one that supports all of Vista’s features, consider getting a newer model. In any case, if you’re experiencing this problem, leave a comment letting everyone know what’s working and not working, perhaps you can help someone else as well.