[CentOS-virt] xenbr0 isn't created anymore

Tue Apr 1 13:12:49 UTC 2008
Kai Schaetzl <maillists at conactive.com>

Ross S. W. Walker wrote on Mon, 31 Mar 2008 17:45:24 -0400:

> It's not all port 67, the DHCP client sends DHCPREQ via UDP port 67 to
> the broadcast address UDP port 68, the DHCP server responds with a
> DHCPOFFER from it's IP address UDP port 68 to the clients broadcast
> address UDP port 67.

Ah, many thanks. Ok, what happens is that the request appears on all interfaces 
but the reply goes out on peth0 only. And that never reaches the DomU on vifx.0.
If I start libvirtd and then kill dnsmasq (as I want dhcpd to answer) the reply 
propagates further and DomU takes the IP address. There's obviously something in 
the routing/forwarding that the startup of libvirtd changes. Output of iptables 
-L suggests it adds a forwarding rule to forward from anywhere to anywhere. But 
that's not true. This seems to be a limitation of the iptables -L output: it 
doesn't show the interface (and I don't see a way to change this, if I try to 
specify an interface I get an error that thi9s is not allowed with -L). Well, I 
saved iptables and from that it seems that all the forwarding rules apply to 
virbr0 only. As virbr0 isn't attached to anything anymore these rules should be 
useless. libvirtd also adds NAT rules, but I don't see how these could affect 
this either. So, there might be something else needed.

> BTW I discovered that the tap devices are from qemu running in HVM
> mode. In HVM qemu does the network emulation and uses the kernel
> tun device for creating it's network interfaces.

Ah, I see. I'm not running fully virtualized.
> > Thanks, I have looked at the patches, but they seem to be for something 
> > different. I checked if I can create a new VM with virt-manager and this 
> > fails in the network device step. But I think that's yet another bug, we 
> > already discussed here, there's also a patch for that.
> If you can create a VM with virt-manager, then you don't have Xen 3.2
> installed or properly installed...

no, no, no. "I can create a new VM with virt-manager and this fails in the 
network device step". It cannot get any interfaces. I think there is a patch 
floating around for this, already mentioned on this list, but it's not the patch
(es) you mentioned. Those two patches seem to apply to HVM only, so I shouldn't 
need them. If I wanted to create new VMs with virt-manager I would need to apply 
this other patch, though.

> I never encountered this error.

I feared that :-(

If you upgraded to Xen 3.2 did you upgrade
> both the xen-3.2 and xen-libs-3.2 packages? Did you edit your grub config
> too to load xen-3.2 as well?

Sure. I also installed xen-devel. Ahm, is that "xm new" supposed to do what I 
think or is it doing something else? I mean I understand that "xm new vmname" 
should take the VM of that name (identified by the existing config file of that 
name) and add it to the xenstore, so that I can "manage" from there. Meaning 
being able to use "start" (there's no stop?) and list it even when not running.

> BTW xmlproc is handled completely in xend I believe, it all works
> fine on my host and I have no python-xml installed!

Hm, may need to subscribe to the xen list ;-)


Kai Schätzl, Berlin, Germany
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