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From: Don Bowman <don@sandvine.com>
To: "'Marc G. Fournier'" <scrappy@hub.org>,
	Tim Wilde <twilde@dyndns.org>
Date: Sun, 7 Mar 2004 19:50:44 -0500 
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cc: freebsd-net@freebsd.org
Subject: RE: Odd network issue ... *very* slow scp between two servers 
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From: Marc G. Fournier [mailto:scrappy@hub.org]
> On Sat, 6 Mar 2004, Tim Wilde wrote:
> 
> > On Sat, 6 Mar 2004, Marc G. Fournier wrote:
> >
> > > I have two servers on the same network switch, sitting 
> one on top of the
> > > other ... one is running an em (Dual-Xeon 2.4Ghz) device, 
> the other an fxp
> > > (Dual-PIII 1.3Ghz) device ...
> >
> > Is it a Cisco Catalyst switch?  If so, you need to switch 
> the em's to
> > autoselect, on both the server and switch end.  For some 
> reason, the em
> > driver will not properly lock down its rate when talking to a Cisco
> > Catalyst switch.  At least, I had an identical problem with 
> em's talking
> > to a Catalyst 2950 and that was the fix I came up with.  
> Give it a try and
> > see how your results go.
> 
> Note that forcing it to 100baseT half-duplex (or 10baseT/UTP 
> half-duplex)
> corrects the problem ... turns out it is only in full-duplex 
> mode that its
> hosed ...

Actually, this is normal behaviour according to the 802.3u spec.
If a device in 'auto' mode is connected to one that is
forced 100FDX, the auto one will negotiate 100HDX.

For example, see HP faq:
http://www.hp.com/rnd/support/faqs/2700.htm#question6

http://roger.friendex.net/duplex_mismatch.htm
has a nice table of this.

--don