Re: Issues with eepro100 and full duplex

On 14 Aug 2003, Devin Heitmueller wrote:

> > > Then I use mii-tool to configure the card to disable autonegotiate and
> > > run at 100 full duplex.  Mii-tool reports that the card is running at
..
> > That's exactly what is expected.  You have just created a duplex
> > mismatch, which as a flawed configuration.
> 
> Does this mean that if I hard-coded both ends to run at 100 full duplex,
> that I would end up with 100 half duplex being the end result?  

No, you would have a working, _non-standard_, 100Mbps full duplex link.

And the next person that tries to use that switch port or machine will
swear at the *&$#@ that misconfigured the network so that it wouldn't
work with standard-conforming equipment.

> Is the problem that the duplex is only being forced at one end of the
> link?  Or is it that full duplex has been forced at all?

Some would claim that the problem is that only one end was forced.

I claim that the problem is forcing full duplex at all, even if it's
hidden by forcing both ends.  Networks should be plug-and-play, not
configure-by-hand.

> If so, why would there be a setting to set the link to full duplex

Because when full duplex was first introduced, there was no standard and
autonegotiation did not yet exist.  When some switch vendors (rhymes
with Sysco) built hardware with broken autonegotiation, they blamed the
new autonegotiation standard and advised customers to force full
duplex.  So we had to provide the option, even though it was a Very Bad
Idea.

> > Yes.  If autonegotiation does not take place, and it won't with a forced
> > link, the link speed is sensed based on the link beat.
> > Ethernet _is_ CSMA/CD (informally "half duplex"), so you end up with a
> > half duplex connection.
> 
> >From what it sounds like, everything I am seeing is expected behavior,
> which is fine by me.  I am just trying to provide a mechanism that
> allows my customers to configure the product to work with their
> sometimes buggy switching equipment.  If this is how it works, then so
> be it.

Tell them to read
   http://www.cisco.com/warp/public/473/46.html


-- 
Donald Becker				[email protected]
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