[wellylug] Network cards running at 10mb/s instead of 100 - w hy?

[Ewen McNeill]

In message <1066625322.3082.13.camel at damon.asianreflection.com>, Damon Lynch wri
tes:
>On Tue, 2003-10-21 at 06:40, Michael Bordignon wrote:
>> > # mii-tool eth0
>> > eth0: 10 Mbit, half duplex, no link
>> [...]
>
>When I use ssh to transfer files (via konqueror or gftp), I'm getting
>around 1.1 MB / sec, about 1/5th of what you are seeing.

If you're using a Pentium 233, then the crypto overhead for ssh will
make a reasonably significant difference especially if you use triple
DES (3DES) rather than a more CPU efficient alternative like blowfish. 
(I'd expect using 3DES to add 15-20% to the transfer time on a Pentium
233 or slower.)

FTP, HTTP, NFS or similar is a better way of doing "raw" speed tests.
And remember to transfer fairly large files -- 10MB is probably the
minimum for a LAN speed test these days.  TCP/IP in particular needs a
while to get past its "slow start" phase.

You should be able to do better off a 100Mbps card than 1.1MB/sec though,
especially given an efficient transfer protocol.  But perhaps not as
high as you're hoping.

Given the mii-tool output you list I'd be looking at what the card is
plugged into.  100Mbps capable cards will only do 100Mbps if plugged
into a hub/switch that can do 100Mbps.  Full duplex capable cards will
only do full duplex if they are plugged into a switch.  Dual-speed hubs
have two separate hubs, connected with a bridge, and can be rather
inefficient if you have some machines with 10Mbps cards and some with
100Mbps cards.

The fact that the mii-tool output claims there's no link (ie, no link
signal) makes me suspect that you've got the cards plugged into an old,
"dumb" hub, in which case you're not going to see anything better than
10Mbps anyway.

>A machine of Pentium 233 vintage should have PCI slots good enough to
>handle 100mb/s, right?

The PCI slots, yes -- 100Mbps is about 12.5MBps data across the PCI bus;
with a 32-bit bus (eg, PCI) that's about a 4Mhz data rate -- even the
original PCI standard was 33Mhz.

The rest of the architecture probably isn't up to handling 100Mbps at
line rate though.

Ewen