Wireshark-users: Re: [Wireshark-users] 8-10% packet error/loss is normalwired network?
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From: Kok-Yong Tan <ktan@xxxxxxxxxxxxxxxxxxx>
Date: Thu, 12 Jul 2012 18:46:43 -0400
Since the OP didn't mention anything about whether the switch the printer is connected to is manageable or not, I assumed that it's an unmanaged dumb switch with no duplex settings possible (i.e., these are usually set to autonegotiate). Since OP's printer is set to full duplex and has autonegotiation disabled and is directly connected to an autonegotiating switch, that means the port on the switch which OP's printer is connected to will failover into half-duplex. So there's a duplex mismatch right there, no? 

On 7/12/12 18:05, jim@xxxxxxxxxxxxxxxxx wrote:

That is not correct. It would be a good practice to use the same
autonegotiation settings throughout your network, but the printer and the
desktop PC do NOT have to match. Autonegotiation takes place only between
two directly connected NICs. The NIC in the desktop PC must have the same
autonegotiation settings as the port that it is connected to on switch C.
The NIC in the printer must have the same autonegotiation settings as the
port that it is connected to on switch B. The desktop PC and the printer do
not autonegotiate with each other. They do not have a direct physical
connection to each other.

So the printer is set for full duplex with autonegotiation disabled. If the
switch port that it is connected to is also set to full duplex with
autonegotiation disabled, then both sides match and the link will be full
duplex.

The desktop PC has autonegotiation enabled. If the switch port that it is
connected to also has autonegotition enabled, then the two devices SHOULD
negotiate a full duplex connection.

Flako, a duplex mismatch could still be a problem, but you need to check
the desktop PC against the directly connected switch port, not against the
printer; and check the printer against its directly connected switch port,
not against the desktop PC.

In any case, you want to make sure that both links are full duplex; that
is, that all four NICs are set to and actually operating at full duplex. If
one link is half duplex, even if both ends match, it will still have less
throughput than the other link and can result in dropped packets under high
load.

And again, you've got a capacity mismatch between the two switches (100mbps
vs 1 Gbps). If these switches maintains per-port counters, you might want
to check each port for dropped frames.

Original Message:
-----------------
From: Kok-Yong Tan ktan@xxxxxxxxxxxxxxxxxxx
Date: Thu, 12 Jul 2012 17:15:57 -0400
To: wireshark-users@xxxxxxxxxxxxx
Subject: Re: [Wireshark-users] 8-10% packet error/loss is
normalwired	network?


Are your statements above accurate (printer has autonegotiation
*DISABLED* and desktop has autonegotiation *ENABLED*)?  Both devices
*MUST* match, even if one has autonegotiation enabled.  i.e., If the
desktop has autonegotiation enabled, then the printer *MUST ALSO* have
autonegotiation enabled.  Otherwise autonegotiation will fail and the
device with autonegotiation enabled will drop down to half duplex.   See
this:

<http://en.wikipedia.org/wiki/Duplex_mismatch#Duplex_mismatch_due_to_autoneg
otiation>

Hansang Bae mentioned this in a session at a prior Sharkfest during one
of his very illuminating "Deep Dive" packet analysis sessions.

Reality Artisans, Inc.             #   Network Wrangling and Delousing
P.O. Box 565, Gracie Station       #   Apple Certified Consultant
New York, NY 10028-0019            #   Apple Consultants Network member
<http://www.realityartisans.com>     #   Apple Developer Connection member
(212) 369-4876 (Voice)             #   My PGP public key can be found
at<https://keyserver.pgp.com>





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