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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: Pasi Kärkkäinen <pasik@xxxxxx>
Date: Sat, 5 Apr 2008 13:17:39 +0300
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On Fri, Apr 04, 2008 at 10:04:53PM +1100, James Harper 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
> 
> When this happens, Linux appears to not pass the packets beyond the
> vifX.Y interface - a tcpdump on (say) vif455.0 shows packets but a
> tcpdump on eth0 does not show all the packets - packets with a bad
> checksum don't make it that far.
>  
> 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...
> 
> Can someone please confirm that this is a limitation of Linux and/or
> Xen?
> 

What version of Windows has this problem? 

Did you find out anything about it yet? 

-- Pasi


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