netdev - Re: jme: UDP checksum error, and lots of them

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Message-Id: <20101202042820.M98672@cooldavid.org>
Date:	Thu, 2 Dec 2010 12:33:01 +0800
From:	"Guo-Fu Tseng" <cooldavid@...ldavid.org>
To:	David Miller <davem@...emloft.net>, jengelh@...ozas.de
Cc:	netdev@...r.kernel.org
Subject: Re: jme: UDP checksum error, and lots of them

On Wed, 01 Dec 2010 20:09:35 -0800 (PST), David Miller wrote
> From: Jan Engelhardt <jengelh@...ozas.de>
> Date: Thu, 2 Dec 2010 04:39:34 +0100 (CET)
> 
> > Why does the JME driver care so much about this that it needs to print 
> > this for every packet? It does not look like it has any offloading 
> > features.
> 
> Well I'm glad it let us know about the bad checksum which would otherwise
> have been unnoticed.
> 
> Please try to pinpoint why the checksum is bad, because it seems that
> tcpdump agrees with the driver.  Perhaps it's some side effect of how
> vpnc uses TUN/TAP, or something like that.
> 
> Seeing the bad checksum even in tcpdump, and then seeing proper replies
> going back, that is very suspicious and should be looked into.
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Indeed... It is suspicious to reply proper response against the packet
with bad checksum.

Jan: Would you try to turn off the rx-checksum offloading with ethtool
and see how it goes?

I suspect that there might be some the HW-Checksum behavior error.
ex: Replaced the UDP checksum field while it's all zero(no need to checksum)

Guo-Fu Tseng

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