From: Dan Stromberg <strombrg@dcs.nac.uci.edu>
Subject: Re: NFS TCP settings
Date: Wed, 21 Dec 2005 11:02:21 -0800
Message-ID: <1135191742.1122.402.camel@seki.nac.uci.edu>
References: <20051221163254.70779.qmail@web34105.mail.mud.yahoo.com>
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Content-Type: text/plain
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>,
	nfs@lists.sourceforge.net, strombrg@dcs.nac.uci.edu
To: Kenny Simpson <theonetruekenny@yahoo.com>
In-Reply-To: <20051221163254.70779.qmail@web34105.mail.mud.yahoo.com>
Sender: nfs-admin@lists.sourceforge.net
Errors-To: nfs-admin@lists.sourceforge.net

On Wed, 2005-12-21 at 08:32 -0800, Kenny Simpson wrote:
> --- Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
> > The NFS/RPC code has no direct control over the TCP window size. That
> > would be an issue for the networking people.
> 
> I have tracked this a bit further, and am reporting back for completeness..
> 
> The version of OnTap we are using (6.4.1p1) does not seem to support RFC 1323 (large TCP windows),
> but the Linux client does.  The window scaling is communicated in the initial connection (SYN), so
> if ethereal does not catch that, it will incorrectly report the window size as the unscaled number
> - making the Linux client appear to be using a very small window.
> The reason it appeared that the small window size was being honored is a result of the direct
> crossover cable making the BDP (bandwidth-delay product) very small.
> 
> As for the server side, because large TCP windows are not supported, the best it can do is 64k -
> which it does.  Running with GbE and jumbo packets fills the window quite fast obviating the need
> for RFC 1323.
> 
> Thanks to those who took the time to swing a clue stick in my direction.

Speaking of TCP Window Scaling...  :)

I have some connection between some pairs of hosts for which all of the
following appear to be true:

1) TCP Window Scaling is enabled on both endpoints
2) TCP Window Scaling is mentioned in the initial SYN and SYN/ACK
3) tcptrace thinks that TCP Window Scaling isn't happening

Is there something other than the SYN and SYN/ACK that might cause TCP
Window Scaling to go away?

(Other than SACK that is - we have that enabled - at least according to
tcptrace)

Thanks!


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