Thanks all, I've learned a great deal more about packet analysis through this experience :)
It is definitely software related. The app I was using is s3sync which is a ruby based rsync style app for S3. I don't think Ruby has the ability to resize the send buffer (at least not that I've found) and this is what was the cause of my issue. I was thrown off by the seemingly small window sizes I was seeing and was sure it was TCP related.
Ruby development is certainly beyond the scope of this list, but at least I know what to look at now! Thanks again!
-----Original Message-----
From: wireshark-users-bounces@xxxxxxxxxxxxx [mailto:wireshark-users-bounces@xxxxxxxxxxxxx] On Behalf Of Sake Blok
Sent: Friday, September 12, 2008 12:34 AM
To: Community support list for Wireshark
Subject: Re: [Wireshark-users] TCP Window Sizes
On Wed, Sep 10, 2008 at 07:23:47PM -0400, Hansang Bae wrote:
> Aaron Allen wrote:
> > My attachments were a bit too large, I have put the attachments
> > referenced below up at this site temporarily:
> > http://216.248.62.108/wireshark/
Great, thanks!
> > I'll admit, I'm confused. I see larger window sizes in the
> > packet captures from the Vista workstation, but not from the
> > Windows 2008 server. The packet captures from the local and
> > SPAN session vary greatly from the Vista machine. Since that
> > NIC has "Large Send Offload" enabled, I'm guessing the
> > workstation NIC is handling segmentation, and thus the differences.
That's exactly what happens.
> > Is it possible that this is an application limitation? I
> > really thought this should all be transparent to the app.
Well, I'm not an expert in how applications interact with the
tcp/ip stack. But it is clear that it is a local problem on
your Win2008 box.
> But the key thing here is the 8192 byte sending buffer by the
> application. Clearly TCP is not at fault here. But then someone in my
> team noticed something. You are doing a PUT from IE correct?
I did not see the "User-Agent" header in the request, is this a custom
application doing the PUT? If so, could you try the same action
from a browser, to see if it makes a difference?
> See: http://support.microsoft.com/kb/329781
>
> The PUT default sending buffer (not to be confused to TCP send buffer)
> defaults to 8192 bytes.
I agree with this, it all looks like the application is using a fixed
8K send buffer, so it is not able to fully utilize the tcp window
that Amazon advertises.
Cheers,
Sake
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