[c-nsp] does duplex mismatch affect UDP throughput?

[Gert Doering]

Hi,

On Sun, Jul 24, 2011 at 04:52:33AM +0300, Martin T wrote:
> WS-C2950C-24 port Fa0/1 is configured to "speed 100" and "duplex full":
> 
> Fa0/1     -> PE860           connected    1            full    100 10/100BaseTX
>
> ..and as PE860 eth0 interface is configured to autonegotiate it's
> speed, there is a duplex mismatch between the switch and PE860
> machine.

Of course.  So just don't do that.  Never configure anything for 
"autonegotiation off" unless you know for sure that one of the devices
will not do autonegotiation properly (which is nowadays basically 
"the single-port fastethernet ports on cisco 7200s", "telco gear", and 
nothing else).

> I configured IP address 10.10.10.1 to eth0 of T60 and 10.10.10.2 to
> eth0 of PE860. There is no packet loss between the T60 and PE860 if
> there is no traffic other than ICMP "echo requests" and "echo replies"
> between the hosts:

This is not surprising.  Packet loss will hit if both sides want to send
traffic at the same time - the "full duplex" side will just send it, while
the "half duplex" side will detect it as "late collision" and drop both
packets.

Ping is strictly request/response, with only one packet ever in-flight 
at the same time, so no problems here.

Try two parallel ping streams with "ping -i 0.01 -s 1000" and you'll see 
loss.

[..]
> So I guess duplex mismatch does affect UDP traffic as well? >

Sure.  It breaks *Ethernet* traffic, no matter what's in there.

gert
-- 
USENET is *not* the non-clickable part of WWW!
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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