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
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.
-Mike
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