[tulip] strange speed&duplex? (accton en 2242)

Donald Becker becker@scyld.com
Wed, 11 Apr 2001 08:55:27 -0400 (EDT)

On Wed, 11 Apr 2001, Erik Steffl wrote:

> Donald Becker wrote:
> ...
> > > # ./mii-diag
> > > Using the default interface 'eth0'.
> > > Basic registers of MII PHY #1:  1000 786d 0022 5410 01e1 40a1 0005 2801.
> > >  Basic mode control register 0x1000: Auto-negotiation enabled.
> > >  You have link beat, and everything is working OK.
> > >  Your link partner advertised 40a1: 100baseTx 10baseT.
> > 
> > Your link partner is a half duplex bridged repeater.
> > It cannot do full duplex.
> > If you force full duplex, you will have very bad performance.
> > 
> > The new version of 'mii-diag' calculates the speed and duplex for you.
> > With the older versions you have to manually interpret the highest
> > common capability.
>   how do I find out what speed is actually used and whether it's FD or
> HD? I checked the docs for mii-diag on scyld.com but it all seems to
> refer to capabilities, not the actual settings.

The speed used is the highest common capability.  In this case
100baseTx ("half duplex").  Ethernet is CSMA/CD "half duplex" unless
explicitly noted as full duplex.

More details are at

>   the link partner is a D-Link DSH-5 hub with switch (dual speed,
> 10/100Mbps),

That's a dual speed repeater, with a bridge between the two repeater

> it says it can operate different speeds on different
> ports... it has a EXP-FDX led which is on and description says:
> expansion switch full duplex status. I thought it means it operates in
> full duplex mode but I guess it only means that up-link (port that can
> connect this one to another hub) is capable of FD (or something else,
> not sure what expansion port is).

I looked this up:
You can switch one of the ports to talk full duplex directly to the
bridge/switch port if you give up the dual-speed nature of the repeater.

>   I have two other computers connected to the same hub, one says it's
> half duplex (ms win machine) and the other says:

More the cables and you'll find that only one port is full duplex, and
only when the special switch is set to "expansion".

>   I guess I need a different hub/switch - how do I find out whether it's
> full duplex (on all ports)? I checked the docs again and it does not
> mention whether ist's FD or HD anywhere - does it mean that unless it

Read the D-Link web page to understand what your bridged repeater is doing.

> > > Index #1: Found a Accton EN1217/EN2242 (ADMtek Comet) adapter at 0x1c00.
> > >  Comet duplex is reported in the MII status registers.
> > Take careful note of this message!
>  why? what does it mean? What does Comet duplex mean?

The duplex that the Comet chip is operating at.

Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993