[Xen-devel] Linux TCP Checksum offload limitations

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

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?

Thanks

James

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