Subject: Re: full duplex ethernet trouble
To: Dave <>
From: Gilbert Fernandes <>
List: tech-userlevel
Date: 05/06/2004 12:34:46
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.

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).

> 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.

>         address: 00:a0:cc:d1:ce:ef
>         media: Ethernet 100baseTX full-duplex
>         status: active
>         inet netmask 0xffffff00 broadcast
>         inet6 fe80::2a0:ccff:fed1:ceef%tlp0 prefixlen 64 scopeid 0x1
> # cat /etc/ifconfig.tlp0
> netmask 0xffffff00 media 100baseTX
> [note: appending "mediaopt full-duplex" made no difference.]

according to your ifconfig output, i'm right.
you are mixing full duplex with a non full-duplex
card. collisions are gonna happen (you see the light
blink in yellow while you transmit, don't you ?)

if both your cards do not support full duplex, please
remain 100baseTX only.

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

have a moo day :)

Gilbert Fernandes