eepro100 confusion

Donald Becker becker at
Thu Oct 24 13:07:11 PDT 2002

On Thu, 24 Oct 2002, Michael Stein wrote:

> > I recently had two IBM Linux clusters installed at my work site. Due to
> > certain customer issues, our cisco switches have all ports set to 100Mbits
> > Full Duplex for all server connections.
> My understanding is that setting ports to 100 Mbits/full duplex will
> PREVENT the NICs from negotiating thus requiring specifying the matching
> values on every server NIC.

Correct.  To repeat the point: forcing full duplex will turn off
autonegotiation, and often link speed sensing.

> If not specified on the server the server should, without negotiating,
> default to half-duplex, thus resulting in a duplex mismatch.


> There might have been a time years ago when FE negotiating was a problem,
> but shouldn't we be way past that by now?

I answer questions relating to this issue every day.
The problem sites are those with Cisco switches and administrators with
Cisco training.

Cisco switches had a broken autonegotiation implementation.  Rather than
fix the deployed hardware, Cisco taught that autonegotiation was
unreliable and should be turned off.  OK.  But they went further and
recommended forcing full duplex.

> This maximizes the effort/support needed on each and every server.

That's the big problem.  The result is that every connected machine must
now be specifically configured.  Rather than having plug-and-play
computing resources that work out of the box, you need installation
people that understand the configuration specifics of each device.

Donald Becker				becker at
Scyld Computing Corporation
410 Severn Ave. Suite 210		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993

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