Re: [PATCH] lro: IP fragment checking

From: Andrew Gallatin
Date: Mon Dec 01 2008 - 19:02:50 EST

Ben Hutchings wrote:
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
What hardware does an explicit check for fragmentation?

Any that implements TCP/UDP checksumming properly.

How many do?

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.

We do partial checksums.

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