Bit-Shift.Net

Every once in a while I would notice certain web sites taking a long time to load. I had blamed it on network congestion and my

less than optimal Internet connection. But a short while ago I upgraded my Internet connection to Verizon's FIOS. Having previously had FIOS I knew I shouldn't have any more issues with network congestion.

After the upgrade I set about doing the usual network performance tests. Once satisfied I was getting the bandwidth I had purchased I set about my normal routine. But even with the upgraded Internet connection I was still noticing some lagginess on certain web sites. It was tolerable so I didn't pay much attention to it.

A few days ago, LifeHacker blog, ran an article about a new feature in Windows Vista called Auto-Tuning. The idea behind this feature is that in the days of old, modems and network equipment could only handle receiving a certain amount of data before they became overwhelmed, this is referred to as the receive window. Newer networking equipment is able to handle receiving considerable larger amounts of information without becoming overwhelmed.

According to the Windows Core Networking blog, the Auto-Tuning feature takes certain conditions into account like bandwidth, network delay and application delay and automatically adjusts this window to maximize performance. The problem lies in that older firewalls & routers can't properly handle the automatic resizing of the receiving window and cause considerable slow downs or application crashes.

To correct the problem, there are a number of steps you can take:

If your connection from a Vista machine appears slow or hung, here are some steps to isolate the cause:

• First, make sure that your firewall and router can support window scaling. Some devices from Linksys, Cisco, NetApp, SonicWall, Netgear, Checkpoint, D-Link were reported as having problems with window scaling. (Some of the incompatible devices are given here. You can check with the manufacturer or run the connectivity diagnostic suite (especially, TCP High Performance Test) provided by Microsoft to determine your gateway device’s compliance.
• Second, check with the manufacturer if a firmware update has been issued for your device that can fix the problem. Replace the problematic device or update the firmware as suggested by the manufacturer. If the router cannot be replaced or if it the device is remote (e.g., a firewall of your ISP or corporation)
• Third, If the problem still persists, you can restrict autotuning by running “netsh interface tcp set global autotuninglevel=restricted” from the command prompt. We have found that restricted mode will often allow some of the benefits of autotuning with a number of problematic devices.
• Lastly, if all else fails, in order to disable this feature, run "netsh interface tcp set global autotuninglevel=disabled".
• (In order to re-enable autotuning, run “netsh interface tcp set global autotuninglevel=normal”.)

You'll have to run the "netsh" commands from a command prompt with elevated privileges. To do so, open the start menu and type "cmd" into the search bar. Then right-click on the cmd program and select Run as Administrator.