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Re: [Xen-devel] Linux TCP Checksum offload limitations

To: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Linux TCP Checksum offload limitations
From: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 7 Apr 2008 00:02:38 +0100
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On Fri, 4 Apr 2008 22:04:53 +1100
"James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

> Some version of Windows appear to give the network adapter driver a
> packet broken up into fairly small pieces, eg
> Page 0: 14 bytes of Ethernet Header
> Page 1: 20 bytes of IP Header
> Page 2: 20 bytes of TCP Header
> Page 3: 1460 bytes of TCP Data

NDIS fragments are nothing to do with the wire side interface

> Our best guess is that the Linux checksum offload code can't cope with
> the way Windows is fragmenting the packets, but maybe Xen is somehow
> involved in this...

Unconnected with Linux, Xen bug. Xen is responsible for handling NDIS s/g
lists on the windows side and turning them into a single virtual network

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