Wireshark-users: Re: [Wireshark-users] TCP Window Sizes

From: Hansang Bae <hbae@xxxxxxxxxx>
Date: Mon, 08 Sep 2008 21:42:22 -0400

Aaron Allen wrote:

This is primarily a TCP related question, so if there is a more appropriate forum for this question, please point me in the right direction.

I am trying to identify the source of a slowdown for an upload to Amazon S3 from a Windows 2008 server. Packet captures seem to indicate the problem is with the TCP window size. When I manually increase the TCP window size on another machine, I am easily able to get maximum bandwidth utilization. But, for some reason, this 2008 machine won’t increase the window size beyond 64K.

I can’t increase the TCP Window size on the 2008 machine because of the new and “improved” auto tcp tuning. Is there something else I should be looking for that could be causing the window size to not be scaled any higher?

Are you sure it's not using RFC1323? Do you have a sample trace that you can upload (in pcap format). TCP setup and a few sampling during the upload will be fine. Maybe it's scaling and you're not looking at the scaling factor?

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Thanks,
Hansang