From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Chin <dwchin@umich.edu>
Subject: Re: setting duplex mode on ethernet cards
Date: Mon, 17 Jun 2002 12:34:41 -0400
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In message <15630.2559.914232.169038@cerise.nosuchdomain.co.uk>, Glynn Clements
 writes:
> 
> Paul Furness wrote:
> 
> > Thanks, and thanks to everyone who made some suggestions.
> > 
> > mii-tool worked just great to tell me what I was using (100M HD) and
> > putting:
> > 
> > options 3c59x full_duplex=1
> > 
> > in /etc/modules.conf persuaded the card to go at 100M FD.
> 
> Are you aware that forcing full-duplex is usually the wrong thing to
> do?
> 
> If the network is switched, full-duplex should get enabled
> automatically. If the network isn't switched, enabling full-duplex
> will usually have an adverse effect upon performance, due to
> collisions.

Not necessarily:  The departmental 100baseT switch where I am is old and 
does not auto-negotiate duplex settings.  There is a physical switch on each 
port of the switch that switches duplex settings. (Um, I was at a loss for 
words.)  Anyway, upshot is that I needed to force full-duplex (mii-tool -F 
100baseTx-FD).

But, yes, one must make sure that FD is the appropriate setting.

--Dave