[realtek] MII-DIAG and setting speeds

[Donald Becker]

On Tue, 26 Dec 2000, Ferry van Steen wrote:

> I can't seem to figure out mii-diag properly.
> 
> I had a 10Mbps HUB on my 100Mbps Ethernetcards, everything was functioning
> fine (at 10Mbps) FTPing from my windows to my linux went at almost 1MBps
> (byte) so that was ok. Now I got a 100/10 HUB so I hang that in but the
> card wouldn't auto notice it, so I did mii-diag -F 100baseTx-FD (Full
> Duplex Mode)

This is almost certainly the wrong thing to do.
You disabled autonegotiation by forcing the speed to 100baseTx!

Autonegotiation always works when used with correctly designed hardware.
What did 'mii-diag' report about the link when you _didn't_ force the media
type?

> This seemed to function fine, I could download at 2.5MBps
> now, however when I pulled the wire and plugged it back in the LED on the
> HUB just kept flickering while the PC (IP) was unreachable, which made me
> think renegotiation about the speed went wrong, so I set the card to
> 100baseTx (no duplex), now my downloads go at 100kBps max which isn't
> really what I was looking for. 

Rule: Always leave autonegotiation enabled.

> so I can have max performance? The box of the HUB doesn't mention whether
> or not it's Half-Duplex or Full-Duplex or anything else for that
> matter. Just 10/100 is all it says.... 

Generally a "hub" is a repeater.  A repeater never supports full duplex.
I'm guessing that you have a 10/100 bridged repeater, or a repeater that
switches all ports to the speed of the lowest speed port.  A single 10Mbps
device will drop all ports to 10Mbps.

If the box says "switch", then it might be capable of full duplex.  It will
almost always have a full duplex LED per port.


Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
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