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Re: [Xen-users] could not get IP address for the interface created by netfront driver on HVM guest

  • To: Todd Deshane <todd.deshane@xxxxxxx>
  • From: veerasena reddy <veeruyours@xxxxxxxxx>
  • Date: Fri, 24 Jun 2011 18:01:18 +0530
  • Cc: xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Fri, 24 Jun 2011 05:32:54 -0700
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Thank you very much for the response.
It took little long time as i wanted to do some research from my side before asking you more.

Please find below my observations:
I did tcpdump on Guest and dom0. On both, Guest and dom0, I could see the DHCP request from Guest (eth0) to dom0 (virbr0) and DHCP reply from dom0 (virbr0) to Guest (eth0). Please find below the tcpdump output.

When I assigned a static IP address to eth0 interface on Guest (ifconfig eth0, i am able to ping virbr0 ( on dom0.

And when I explicitly ran dhclient on domU, i observed "5 bad udp checksums in 5 packets" which was causing drop of packets and the DHCP reply observed in tcpdump was not reaching DHCP client.
when i disabled Tx checksum on the dom0 vif corresponding to the netfront on domU, i could successfully get IP address assigned for my interface on Guest.
# ethtool -K vif1.0 tx off  <<<---- executed on dom0

Any idea why the "bad checksum" happening with PV driver? (while everything was fine with pure HVM).

Thanks & Regards,

On Sun, Jun 19, 2011 at 6:49 AM, Todd Deshane <todd.deshane@xxxxxxx> wrote:
On Sat, Jun 18, 2011 at 4:16 PM, veerasena reddy <veeruyours@xxxxxxxxx> wrote:
> Hi,
> I am trying to run PV drivers on my HVM guest.
> For this, I have compiled kernel downloaded from kernel.org + the
> PV-on-HVM drivers patch "pvdrivers.20100509-1955.patch" downloaded from
> http://blog.alex.org.uk/2010/05/09/linux-pv-drivers-for-xen-hvm-building-normally-within-an-arbitrary-kernel-tree/.
> During compilation i disabled "Paravirtualized Guest Support" (and so
> "CONFIG_XEN" got disabled) and enabled only "XEN pvdrivers" from the patch.
> The installation of the VM was done using "virt-manager" graphical utility.
> After the installation of VM and the new kernel with PV drivers
> compiled/installed on HVM guest, I shutdown the VM, closed the virt-manager,
> changed the "vif" configuration in /var/lib/xend/domains/<UUID>/config.sxp
> to "(type netfront)" as below:
>     (device
>         (vif
>             (bridge virbr0)
>             (uuid 50c7ccfd-45a7-61df-e94b-52bea67d3ee0)
>             (script /etc/xen/scripts/vif-bridge)
>             (mac 00:16:36:30:24:8a)
>             (type netfront)
>             (backend 0)
>         )
>     )
> Then, xend was restarted and virt-manager is restarted and the HVM guest is
> started.
> The HVM guest boots fine, all the PV drivers are loaded (balloon, vbd, vnif,
> platform-pci), network interface is created (also observed Tx/Rx counters
> increasing) but it never got IP addresses which otherwise could get in pure
> HVM mode. ethtool -i eth0 on the HVM guest shows netfront is the driver for
> the interface.
> Could you please help me, if I missed something in configuring netfront
> device assignment to HVM guest.

IP address assignment should be independent of the NIC driver. Could
you do a tcpdump or tshark network trace to see if the DHCP packets
are going and coming in correctly?

You could also try to assign a static IP to and pinging self and the
local network/gateway to see if basic networking is working.


> Thanks & Regards,
> VSR.
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users

Todd Deshane

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