[c-nsp] full duplex mismatch speed - dynamips

[Gert Doering]

Hi,

On Fri, Aug 20, 2010 at 10:03:12AM +0100, Heath Jones wrote:
> You response appreciated. One fatal assumption though is me only forcing one
> end of the link - where did that come from? Read back over my post, keeping
> in mind that I force both ends to 100/full.

If you can ensure(!) that both ends are always force-config'ed, then 
there is nothing wrong with forcing 100/full (except for those devices
where that doesn't really work, unfortunately, there's a number of them).

The problem is that networks change.  A server/router breaks down, gets
exchanged in the middle of the night.  Configuration can not be copy-paste'd
(because it's different hardware), so "duplex full" gets lost.

These things happen, and in my experience, if a network runs for 5 years,
you have lots and lots of duplex mismatches creep into your network in
various places - we took over a larger hosting business some years ago,
and they had been religiously nailing "manual forced full-duplex!!" 
everywhere.  I found at least 10 customer connections that had 
developed duplex mismatches over time...

[..]
> Do you have a view on what causes an end (or both ends) of a link to all of
> a sudden change state and think the other end is not capable of 100/full?
> That is what I am trying to understand. I am also referring to a link that
> is not erroring like mad and the occurrences might be as low as once per
> week.

Never seen that.  But that could be cabling that "just barely so" works,
and if something changes (humidity, ...) tolerance is exceeded...

gert
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
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