AutoTuning In Vista Maybe Not Ready For Prime Time

As you surf the web, you will be in conversation with dozens of web servers, and each conversation might have different latency and stability issues. On a less stable (or low bandwidth) connection, a small Receive Window would be a good idea; on a more stable (or high bandwidth) connection, a larger window gives much better performance. With Windows XP and previous, you were limited to a single Receive Window setting, which would apply to all Internet connections, all of the time.

One of the long awaited features in Windows Vista was the ability for it to dynamically determine the Receive Window size, by individual connection. Receive Window Auto-Tuning is one of the many significant improvements in Windows Vista, in my opinion.

For a few owners of computers running Windows Vista, connectivity to the local network, or the Internet, may be problematic. Symptoms are very like the well known MTU Setting problem - some servers, some of the time, can't be contacted, or give poor performance. Copying files locally, from one computer to another, may be fast in one direction, and agonizingly slow in another.

But we know that your local network isn't running through a router, so how would an MTU setting affect your local connection?

The MTU isn't always the culprit in this case. If you have an older firewall or router, that doesn't support Windows Scaling (an essential component in Receive Window Auto-Tuning), you may have this problem. Apparently the lack of Windows Scaling can affect local performance too.

If you are faced by symptoms like an MTU setting problem, that involve a computer running Windows Vista, first try disabling Auto-Tuning. In a Vista command window (Run as Admin), enter

netsh interface tcp set global autotuning=disabled
netsh interface tcp set global autotuninglevel=disabled

Then shutdown and restart.

Try Internet access with Auto-Tuning shut off, and see if things stabilise. If they do, see if you can upgrade or replace your router. Check with the vendor, and see if a firmware update is available; if not, consider replacing the router. If your router is incapable of supporting Windows Scaling, it may lack other features that you will also enjoy.

Besides RWin AutoTuning, look at other possible problems with Windows Scaling, in Windows Vista and Scalable Networking.

If you see no improvement in your symptoms, turn Auto-Tuning back on before making other changes. Layered Troubleshooting principles suggest one change at a time.
netsh interface tcp set global autotuning=normal
netsh interface tcp set global autotuninglevel=normal

Note the lexicographical variations expressed, above. Some experts state that the relevant keyword is "autotuning", others state "autotuninglevel". There is also a confusion about the value for "autotuning" / "autotuninglevel", which may be either "enabled" or "normal". I suspect that there are two possibilities, "autotuning=enabled" and "autotuninglevel=normal", but I haven't found an authoritative reference, discussing the possibilities.

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WTF-over said...

Considering the Title and subject of this article...I think it is reasonable to expect MS to repair their New OS rather than expect most of their customers to buy a new router. To suggest that is the ultimate in MS arrogance.

In the mean time do not upgrade until the third service pack is available. MS product is usually not stable until then judging by past OS offerings. If you upgrade your laptop and are forced to use Vista....use the COA from your previous XP Laptop and install XP on your new Laptop. Or Switch to Linux both will solve your Vista problems.

Maybe if enough people respond in this manner MS will fix their buggy OS instead of having us pay for the priviledge of Beta testing it for them.

I am sure most of these problems will be repaired when we are expected to Pay for our upgrade to Vista SR2

Best Regards,


Mousky said...

I second WTF-Over comments. I'm getting fed up with this arrogant attitude that people purchase new hardware.

My router works perfectly with my four-year old laptop with XP Home SP2. The internet flies, even over a wireless connection (and were talking 802.11b). Never had any problems with the internet connection.

Meanwhile, my wired connection to my brand new desktop running Vista Home Premium, is a love-hate (mostly hate) relationship. The NIC is Vista Ready. The Internet Connectivity Evaluation tool gives my router a thumbs up save or uPnP (which is disabled). So, according to MS, everything should work like a charm. It doesn't. Downloads are horribly slow.

Stop blaming hardware that works in XP, but does not work in Vista. Numerous MS-MVPs and KB titles word the problem as "Router incompatible with Vista". That's incorrect. It should be "Vista incompatible with Router".

On paper, the new TCP/IP stack sounds great, but there should be some form of backward-compatibility to make it function like the XP SP2 TCP/IP stack. Why would I want to replace a router that works well under XP? Why should I spend anywhere from $50 to $300 to solve a problem in the OS?

Chuck said...


The new IP stack has backward-compatibility. Just disable RWin AutoTuning. RWin AutoTuning requires Windows Scaling, that your router apparently doesn't have. That's probably why your downloads are horribly slow.

And I understand your reluctance to replace something that works fine under Windows XP. But XP doesn't have RWin AutoTuning. RWAT is a major step forward for folks with super fast broadband (which unfortunately doesn't include me 8-{ ).

You can look at it either way - glass half empty, or half full. Vista has new features. New features require new hardware. A new router that supports RWAT will cost the same as 1 or 2 months broadband, and you'll be better prepared for the future.