Subject: Re: full duplex ethernet trouble
To: Gilbert Fernandes <>
From: Dave <>
List: tech-userlevel
Date: 05/06/2004 10:27:10
On Thu, 6 May 2004, Gilbert Fernandes wrote:

> On Wed, May 05, 2004 at 05:44:14PM -0700, Dave wrote:
> > 1) What is the reason for the odd behavior of the
> > full-duplex lights on the switch?
> i have that switch and it does not have "full duplex"
> lights. you have, for each plug, two lights. the first
> one tells if there's a device on that line (electrical
> signal) and the second one is off when it's 10 mbit,
> and turned on when it's 100 mbit. that's all.

This is a newer FS108 switch (automatic uplink detect).  The rightmost
jack has its two light labeled "connect" on the left and "FDX" on the
right.  According to the manual, this label is valid for all jacks.

> the other indicators are green when tx/rx and yellow
> when a collision occurs (on such a switch, this will
> happen if you have one card set as 100baseTX while the
> other is 100baseTX full-duplex).

These indicators are in a bank to the left of the jacks.  Top row
represents 100baseTX usage.  Bottom row represents traffic (yellow for

> > 2) Why when any or both of these lights are on is
> > the network performance exceedingly slow?
> check that both your cards are indeed set as full-duplex.
> if you are mixing full-duplex with non full duplex
> you will get around 6 to 8 mb/s while in fulll duplex
> mode you will get near 12.5 mb/s all the time.

Through trial and error, I determined the problem had to do with incorrect
settings in /etc/ifconfig.tlp0.

> > tlp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> >         address: 00:a0:cc:d1:ce:ef
> >         media: Ethernet 100baseTX full-duplex
Both machines looked like this.

> i can reproduce your problem by mixing full with non-full
> duplex and reproduce the rate problem you talk about.

Since both cards on the network were the same make and model and both had
identical /etc/ifconfig.tlp0 contents, that can't be right.  Using
"auto" in place of "100baseTX" cleared up all the problems.

David Griffith