RE: bifurcated results from netperf

Krasinski, Linda M (
Fri, 16 Apr 1999 13:39:01 -0400

A few weeks ago I investigated a similar situation. Sometimes I got 96Mbs
and sometimes as low as 1Mbs.
My problem was Half vs Full duplex (or shall I say Full vs Auto NIC
settings). The switch was (sometimes) changing to half duplex when the NIC
was set to Full. When the NIC was set to AUTO, I always stayed at Full and
the flaky performance problem never occurred. Pulling a NIC plug out and in
again seemed to cause "noise" which confused my switch and caused it to
change to Half duplex. Sometimes an (experimental) NIC was causing the
noise without the need to pull & plug. If I restarted the systems involved,
without touching any plugs, I usually got a good result. (This was my
observations and conclusion.)

Good Luck!

-----Original Message-----
From: Greg Tillman [mailto:GTILLMAN@MAINE.EDU]
Sent: Monday, April 12, 1999 2:24 PM
To: Roelof JT Jonkman;
Subject: Re: bifurcated results from netperf

>Not to helpfull, but that is sort of the stuff I would go after.
>(well first do what Rick said though, netstat.)
>To get my idea of your config straight:
>Two machines running netperf, interconnected with another dual interface

Sorry, I should have made that clearer. The setup originally was 3

boxa ------ | router-card-a router-card-b | ----- boxb

Where boxa and boxb are each connected to the router box with a crossover
cable. It's about as simple as you can get to test a router, but right now
I'm just running tests between boxa and router-card-a, in hopes of getting
a repeatable measure of thruput. The router box has the second network
card in and working, but nothing plugged into it.

So routing shouldn't enter into it. Duplex shouldn't either, really; I
think the cards are at half duplex by default, but I'll double check
anyway. And no packets are being dropped, according to ifconfig. Also, it
happens in both directions, and it happens between router-card-b and boxb
as well, when I plug that in, and for that matter between boxa and boxb, in
both directions, if I string a crossover cable all the way across.

I am in the process of exploring all suggestions, and thank you all very
much for the feedback. Additional ideas are still quite welcome. I
confess I was hoping someone would just tell me to tweak a kernel setting,
but I guess I'll keep plugging away.

Thanks again

- greg tillman