[Xen-users] problems with csum

[David P Olshefski <olshef@xxxxxxxxxx>]

After booting two VMs on two separate
physical machines, all works fine, and I can execute iperf to obtain about
923Mbps over the Gb link which connects the two physical
hosts.

After applying a few simple iptable
rules to perform DNAT and SNAT in dom0, the performance dropped to 500Kbps.....looking
at the packet stream using ethereal, I found that
the packets had csum errors (hence lots
of retransmissions).  The errors are in the TCP check sum (IP csum
was fine).  

It seems like the problem goes away
when I turn off csum offload inside the VM:

        domU>
  ethtool -K eth0 tx off

Can anyone shed some light on this for
me?

Dave O.
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