SOS - why does an application work fine with a hub but not a switch box?

From: L (lx2828_at_sina.com)
Date: 08/26/03 

Date: Mon, 25 Aug 2003 18:27:51 -0500

Hi,

I would highly appreciate it if someone could help me on this, or give me
some hints.

We are working on a Linux kernel driver that is compiled with the Linux
kernel's 10/100 Ethernet supporting files (pcnet32.c, ns83820.c, etc.), so
the driver running on a target machine can talk to a host machine over the
Ethernet. The target machine's 10/100 port is connected to the 10/100 port
of a host machine that runs the IO stress tests through the Ethernet
connection.

(1) When we connect the target machine with the host machine by using a
network hub, the throughput between the target and the host is around
9.5MB/sec, which has saturated the bandwidth of the 10/100 port (this is
good and what we expected).

(2) When we connect both the target and the host machines by using a switch
box, the throughput drops to 2MB/sec.

(3) When we connect both the target and the host machines directely by using
a crossover Ethernect cable, the throughput is around 1.5MB/sec.

What could be wrong with it? Do we need to modify the original Linux kernel
Ethernet supporting files, or do we need to setup something? We have tried
different switch boxes with different setups (e.g. turn on port fast, etc.),
but didn't get any improvement.

Thanks,

T.

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