On Tue, May 08, 2007 at 12:41:02PM -0500, Mike McGrath wrote:
Daniel P. Berrange wrote:
>On Tue, May 08, 2007 at 11:39:14AM -0500, Mike McGrath wrote:
>
>>We're using xen heavily in Fedora's Infrastructure and presently a
>>number of the xen domU hosts are experiencing terrible checksum issues.
>>I've tried the ethtool -K eth0 tx off fix and it didn't work.
>
>What sort of network config have you got with these ? Briding straight
>to physical device, or NAT'd ?
Bridge
That's good - should avoid the NAT related bugs there then.
>There are a couple issues at play:
>
> - There is a general bug in 2.6.20 that breaks checksum offload
> when used with NAT.
> - In 2.6.19 or later Dom0 will transmits to guests using checksum
> offload, so DHCP client in the guest will mistakenly thing it
> has a corrupt checksum.
>
>To address the first bug requires disabling checksum offload in the eth0 in
>the guest. ethtool -K eth0 tx off in the guest should do it.
>
>To address the 2nd is really difficult since the FC6 install images
>themsves
>have a broken DHCP client for example, so we need to workaround it in the
>kernel. This can be done by disabling checksums on the device in Dom0 - any
>of vifN.0, xenbr0, phet0 should have ethtook -K <dev> tx off done.
>
>NB, ignore eth0 in Dom0, that's a fake device so turning off tx on that
>does
>not fix things.
>
>So in summary, to get it working in general case requires:
>
> ethtool -K eth0 tx off in guest
>
>And
>
> ethtool -K <dev> tx off on whatever bridge device the guest is
> attached to
>
I've actually run that on every interface on every dom[0,U] on the box
:). I've also tried it on two other hosts. One a RHEL5 dom0 and the
other had different hardware but was also a FC6 dom0. I can arrange
access to the box if you're interested.
Ok that makes absolutely no sense to me now :-) Everytime I hit it I was
able to solve it eventually by setting 'tx off' on some combo of devices.
The RHEL-5 Dom0 kernel also already has the neccessary fixes in which is
even odder that it doesn't work for you.
Dan.
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