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[Xen-users] Re: network: bridging problem accessing domU from dom0

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Re: network: bridging problem accessing domU from dom0
From: Jan Niehusmann <jan@xxxxxxxxxx>
Date: Wed, 18 Jan 2006 16:27:42 +0100
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Moritz Bunkus wrote:
> - The dom0 now sends its first "real" data packet -- but from this point
>   on no packets are ever ACKed by the "server1" domU. However, the tcpdump
>   running on the dumU does see those packets! So they are arriving
>   there, but they somehow seem not to be picked up by the kernel... And
>   I have no clue whatsoever why this happens.

This very much looks like the bad tcp checksum problem. You can verify
this with tcpdump -vv, which should show you if the checksum is invalid.

If this is really your problem, you could try turning off tcp checksum
offloading with 'ethtool -K eth0 tx off' (replace eth0 with the
respective interface). Unfortunately, the loopback-device used in dom0
to create dom0's virtual interfaces doesn't support this yet, unlike the
netback/netfront interface connecting domUs to dom0. I sent a patch to
xen-devel to add this feature to dom0 a few days ago.

Jan


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