Re: [Xen-devel] UDP checksums broken in Dom0 -> DomU vif transfer

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

On Mon, Dec 19, 2011 at 04:20:17PM +0100, Michal Suchanek wrote:
> On 19 December 2011 15:29, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> wrote:
> > On Mon, Dec 19, 2011 at 10:27:36AM +0100, Michal Suchanek wrote:
> >> Hello,
> >>
> >> when I boot DomU which uses DHCP to configure IPv4 address it does
> >
> > You didn't say what version of DomU you are running? Is it 3.1?
> 
> I have this problem in 2.6.32 and 3.1 kernels.

Ok. Lets concentrate on 3.1 then.
> 
> >> never get a lease.
> >>
> >> The packets travel to Dom0 where the dhcp server receives them, sends
> >> a reply, that travels to DomU where dhclient receives it, says the
> >> checksum is invalid, and discards it.
> >>
> >> The problem is documented here:
> >>
> >> http://old-list-archives.xen.org/archives/html/xen-users/2006-02/msg00152.html
> >> http://old-list-archives.xen.org/archives/html/xen-devel/2011-04/msg01235.html
> >> http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1655
> >>
> >> The fix is to turn off UDP checksum offloading on the vif interface in
> >> Dom0 as documented in the above mail:
> >>
> >> I edited /etc/xen/scripts/network-bridge,
> >> adding this command to the end of the op_start() function:
> >>
> >> ?? ?? ?? ?? add_to_bridge2 ${bridge} ${pdev}
> >> ?? ?? ?? ?? do_ifup ${netdev}
> >> + ?? ?? ?? # disable ip checksum offloading for veth device
> >> + ?? ?? ?? ethtool -K ${netdev} tx off
> >> ?? ?? else
> >> ?? ?? ?? ?? # old style without ${vdev}
> >>
> >> Note: I am not sure which path is taken through the script, I set the
> >> parameter manually with ethtool before I found this patch.
> >>
> >> It some solutions suggest to turn off UDP checksum offloading in the
> >> DomU as well but it does not seem to be necessary since the packets
> >> would travel to the dhcp server and it would reply to them.
> >>
> >> Some people say this is working for them.
> >>
> >> I suspect this is because some Linux distributions already carry this 
> >> patch.
> >>
> >> Any reason why this can't be fixed in Xen upstream?
> >
> > It should be fixed in the kernel and I think it is fixed. Did you have
> > this problem with a 3.1 or 3.0 kernel?
> 
> Apparently it is not fixed.
> 
> Do you have hash of the Linux upstream commit that fixes it?

Ah, my appoligies - we do not have the fix, albeit I thought I saw the
fix some point. Ian might know since he is the maintainer of
xen-netback.

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