how to force half duplex mode?

[Lawrence Walton]

On Wed, Jan 26, 2000 at 06:25:19PM -0500, James Ralston wrote:
> Hello all,
> 
> I apologize if this question has been answered already, but Greg
> Siekas's archives (as referenced by the vortex web page) don't seem to
> exist.
> 
> I have a 3Com Boomerang (3c900b) NIC.  It's connected to an Asante
> FriendlyNet FS4000P 8-port switch, which performs 10/100Mbps half/full
> duplex auto-negotiation.
> 
> I am trying to figure out how to tell the 3c59x driver to force the
> Boomerang card to half duplex operation.  If it auto-negotiates, it
> will (correctly) negotiate to full duplex, but for testing purposes, I
> want half duplex operation only.  I know that this is possible in
> terms of the hardware of the card, because 3Com's Windows NIC
> Diagnostic Utility could do it (back when 3Com was still shipping it
> with their drivers).
> 
> While passing "full_duplex=1" as a parameter to the driver will force
> full duplex, passing "full_duplex=0" does *not* force half duplex.
> 
> Is there a way to force half duplex operation?
> 
> BTW, if anyone cares, the reason I want to be able to force the card
> to half duplex operation is because after I upgraded both of my home
> machines to Red Hat 6.1 (RPM kernel-2.2.12-20), TCP/IP throughput
> between them dropped into the toilet, to the point where any
> high-throughput TCP/IP links between them (e.g., ftp'ing a file from
> one machine to the other) would practically stall.  (Connections from
> either machine to the outside world (via my DSL line) work fine,
> though.)
> 
> I accidentally wound up creating the state where the NIC on the
> machine that I was transferring the file *from* was operating in full
> duplex, but the switch had that machine's port in half duplex.  This,
> of course, generated a bajillion collisions (due to the duplex
> mismatching), but the transfer between the two machines then zipped
> along at a much more reasonable rate (700kb/sec or so, which is around
> ~5.5Mbps).  So what I'm trying to figure out now is whether the
> collisions were what eliminated the throughout bottleneck (as strange
> as that may sound), or if setting half duplex mode is what did it.
> 
> Thanks,
> James
> 
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Can you set the switch to half duplex?
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