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 ?
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