Re: [PATCH] lro: IP fragment checking

From: Ben Hutchings
Date: Mon Dec 01 2008 - 17:10:09 EST

On Mon, 2008-12-01 at 16:53 -0500, Andrew Gallatin wrote:
> David Miller wrote:
> > From: Andrew Gallatin <gallatin@xxxxxxxx>
> > Date: Mon, 01 Dec 2008 12:50:15 -0500
> >
> >> As to whether or not to do it in the drivers/hardware or in the
> >> LRO code, I favor doing it in the LRO code just so that it is not
> >> missed in some driver.
> >
> > Then there is no point in the hardware doing the check, if
> > we're going to check it anyways.
> >
> > That's part of my point about why this check doesn't belong
> > here.
> What hardware does an explicit check for fragmentation?

Any that implements TCP/UDP checksumming properly.

> In most cases, aren't we just relying on the hardware checksum
> to be wrong on fragmented packets? That works 99.999% of the time,
> but the TCP checksum is pretty weak, and it is possible to
> have a fragmented packet where the first fragment has the same
> checksum as the entire packet.

If your hardware/firmware wrongly claims to be able to verify the
TCP/UDP checksum for an IP fragment, it seems to me you should deal with
that in your driver or fix the firmware.


Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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