On Fri, 20 Aug 2010, Peter Rathlev wrote:
The duplex thing is about Ethernet legacy; you don't have the problem on
fiber links, since these can't be simplex (AFAIK, please correct me if
I'm wrong). But any copper port _might_ be connected to a hub from 1993
some day, and the standard tries to make that work.
I've used AUI-transceivers with 10BASE-FL (fiber) that by definition were
half duplex, but this was in the mid 90:ties so it's doesn't really apply
anymore.
It emulated collissions over the fiber layer as far as I could discern.
+1 on the "use autoneg unless you really have to force duplex".
In case of having to force, do use "speed auto / duplex full" if your
equipment supports it. If you connect something that is "auto / auto" to
it then autoneg still succeeds, if you connect something that is "10/full"
or "100/full" to it, then you still get something that works. If you force
half duplex or connect it to a hub then you'll get a duplex mismatch, but
at least you have a much higher chance of it working even if you do
something wrong.
Duplex seems to be a big mystery in most organizations, I've heard so many
misconceptions about it it's scary, I'd say it's one of the biggest causes
of bad performance in modern networking, at least in equipment which
humans can actually configure. The simple L2 switches with no
configuration is more likely to work.
--
Mikael Abrahamsson email: [email protected]
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