netdev - Re: BSD 4.2 style TCP keepalives

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Message-Id: <20100108.174138.193059500.davem@davemloft.net>
Date:	Fri, 08 Jan 2010 17:41:38 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	nhorman@...driver.com
Cc:	netdev@...r.kernel.org, ilpo.jarvinen@...sinki.fi
Subject: Re: BSD 4.2 style TCP keepalives

From: Neil Horman <nhorman@...driver.com>
Date: Fri, 8 Jan 2010 20:22:27 -0500

> I'm trying to do some independent computation on it, but its looking
> like this may have been a combination of old software (win2k) and a
> bad corner case in hardware.  I think the reporter has a NIC that
> doesn't do TCO properly on these old style keepalives, which would
> explain why it wasn't reproducable outside of the reporters
> environment.  I'm trying to figure out which card/hw revision of NIC
> they were using.  It might be worth coding an errata check into the
> appropriate driver if this all turns out to be accurate to disable
> TCO affectecd hw.

I think it's not a hardware bug, because there isn't anything
interesting about these packets from a checksumming perspective.

It's just a normal 1-byte TCP data frame as far as the card is
concerned.

Rather, I think when checksum offloading, win2k doesn't set the
internal packet state correctly for such probe packets such that the
card is told to checksum the frame.

Ie. a win2k TCP bug and nothing to do with the card or it's driver.
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