Re: Network Performance Issues.

On Sat, Apr 14, 2007 at 11:02:17PM +0100, Alan Chandler wrote:
I have spent all day looking for clues as to how to debug network
performance issues without success. Nobody seems to answered my
previous post on this subject - so I thought I would try again.

The problem I have is this. I have a linux desktop (machine D) siting
on a LAN in my home. This is connected to a linux firewall/nat router
(machine S) with two ethernet cards. One links out to the internet,
the other connects to the internal lan. Connections to the internet
from machine D go through machine S, which acts as a NAT translation. I
do all the control and firewalling using IPTABLES in machine S.

Hi Alan,

I'll answer so you know that you aren't being ignored, but I'm not sure
how much help I'll be.

To summarize, the problem is one of throughput across machine S. From
the net to machine S and from machine S to machine D is fine.

During a download from the net to machine D, what does top on machine S
show? Is it a difficulty of machine S processing packets in on one NIC,
doing the NAT and other firewall rules, and sending them out the second
NIC? When doing either net > S or S > D, it only has to handle one NIC
and no NAT at the same time.

Are the MTUs the same? On the slow path, does machine S have to
disassemble and reassemble ethernet packets? What does ifconfig on
machine S and machine D show? How many packet errors?

Good luck.

Doug.


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