Gigabit Switch

Donald Becker becker at scyld.com
Wed Nov 12 11:46:10 EST 2003


On Tue, 11 Nov 2003 nixon at nsc.liu.se wrote:

> Donald Becker <becker at scyld.com> writes:
> 
> > Frequently "managed" switches are a negative.
> > An Ethernet switch should "just work".
> > Providing configuration options just encourages setting the switch to
> > flawed modes, such as forced-full-duplex or filtering packet types you
> > thought you were not using.
> 
> On the other hand, in the real world autonegotiation doesn't always work.
> And when you get in that spot, it's *very* nice to be able to lock
> down a port's mode.

The only autonegotiation problems I'm aware of is firmware bugs in early
Cisco and 3Com switches.  The switches would autonegotiate, but
sometimes would not notice the parameter changes.

To draw an automotive analogy "sometimes starter motors fail, thus all
cars should have a hand crank in the front".

The proper solution is to replace with working equipment.  A fall back
is to disable autonegotiation and use 10/100 speed sensing half duplex.
A flawed approach (unfortunately the one recommended by Cisco) was to
force speed and full-duplex.

A great thing about autonegotiation is that it is automatic, transparent
and extensible.  Most installations are now using Ethernet flow control.
Because it is configured using autonegotiation, almost no one knows that
they have it.  Things just work better.

-- 
Donald Becker				becker at scyld.com
Scyld Computing Corporation		http://www.scyld.com
914 Bay Ridge Road, Suite 220		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993

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