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

[Michal Suchanek <hramrach@xxxxxxxxxx>]

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.

>> 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:
>>
>> Â Â Â Â add_to_bridge2 ${bridge} ${pdev}
>> Â Â Â Â do_ifup ${netdev}
>> + Â Â Â # disable ip checksum offloading for veth device
>> + Â Â Â ethtool -K ${netdev} tx off
>> Â Â else
>> Â Â Â Â # 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?

Thanks

Michal

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