JeremyWeisser.com

On the surface, Windows Vista’s TCP Auto-Tuning feature sounds like a great idea. For those of you who are not familiar with what it does, the Microsoft Windows Core Networking group describes it in detail.

At any given time, the amount that TCP can send is governed by three factors: the congestion window, the receive window and the number of bytes available to send. Without using TCP window scaling (which is disabled by default in previous versions of Windows), the maximum receive window a receiver can advertise is 64K bytes. Since the congestion window is usually greater than 64K bytes in high-bandwidth/high-latency networks, the receive window is often the limiting factor if the application is submitting enough data. In previous versions of Windows, users can work around this problem by setting the TcpWindowSize registry key value. However, TcpWindowSize is a global setting applied to all connections, and it’s often hard for users to know the appropriate window size to set. To address this issue in Windows Vista, we implemented TCP auto-tuning. It enables TCP window scaling by default and automatically tunes the TCP receive window size based on the bandwidth delay product (BDP) and the rate at which the application reads data from the connection. With TCP auto-tuning, we have seen 1000% (10x) throughput improvements in internal testing over underutilized wide-area network links.

While this all sounds great, practically speaking there are many instances where the auto-tuning feature is more trouble than it’s worth. Due to incompatibilities with certain routers and web sites, the auto-tuning feature may actually bring your browser to a stand-still or even result in a complete crash. Thankfully disabling the feature is pretty painless.

To disable auto-tuning, from the command prompt enter the following line: 

netsh interface tcp set global autotuning=disabled

Should you ever need to re-enable it just use the following command:

netsh interface tcp set global autotuning=normal

For more information about the auto-tuning feature see the Microsoft Windows Core Networking blog post on Advances in Windows Vista TCP/IP.

When managing a Microsoft Exchange 2003 server it is quite easy to determine the mailbox sizes of your various users, just use the ESM (Exchange System Manager). Unfortunately, moving to Exchange 2007 makes this simple task a bit more cumbersome. You must now use the PowerShell to determine mailbox sizes and other statistics. The cmdlet that we will use is Get-MailboxStatistics.

The basic command to return mailbox sizes using the PowerShell is as follows:

Get-MailboxStatistics | FL DisplayName,TotalItemSize,ItemCount

This command will output users display names, their mailbox sizes in bytes and the total item count for the mailbox. Whie this is information is usefull it is not sorted and can’t be filtered. The nice thing about the PowerShell is it’s flexibility. Should we want to return mailbox statistics for all users with more than 100 MB of data in their mailboxes we could run the following command.

Get-MailboxStatistics |where {$_.TotalItemSize -gt 100MB} | sort $_.TotalItemSize |FT DisplayName,TotalItemSize,ItemCount

Should you want this mailbox information sorted you would could use the following command.

Get-MailboxStatistics | Sort-Object TotalItemSize -Descending | ft DisplayName,@{label=”TotalItemSize(KB)”;expression={$_.TotalItemSize.Value.ToKB()}},ItemCount

As you can see, we are now sorting by the TotalItemSize in descending order and telling the PowerShell to return mailbox sizes in KB instead of bytes.

For more information about returning mailbox sizes and statistics in Exchange 2007 see the Microsoft Exchange Server TechCenter.

Another odd IE 7 issues seems to be plaguing many of my client workstations. For some reason, upon launching IE7 the user is greeted with the following error:

“An HTTP error occurred while getting:
http://runonce.msn.com/runonce2.aspx

Details: “connect timed out”. ”

It turns out that the error is the result of a default behavior which can be changed manually. Upon startup, IE is directed to the RunOnce page. To manually change this behavior and skip the RunOnce redirection import the following into your system registry.

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main]“RunOnceHasShown”=dword:00000001

See Microsoft KB article 945385 for more details.