[CentOS-virt] xenbr0 isn't created anymore

Tue Apr 1 15:14:58 UTC 2008
Ross S. W. Walker <rwalker at medallion.com>

Kai Schaetzl wrote:
> Ross S. W. Walker wrote on Tue, 1 Apr 2008 10:16:38 -0400:
> > dnsmasq is going to filter out the incoming dhcp requests as it acts as a
> > dhcp server itself. Try disabling dnsmasq, or move your VMs off of virbr0
> > onto xenbr0.
> I wrote dnsmasq is killed then ;-) I started service libvirtd and then 
> killed dnsmasq and made sure it wasn't running. Then I tried. And the 
> virbr0 is not used anyway. However, something that libvirtd does seems to 
> switch on some extra forwarding that helps the broadcast packet to travel 
> from peth0 to eth0 which otherwise it would only do if it had an IP address 
> target. I have now stopped libvirtd as well and it still works, even for a 
> VM that I start after that (which means I can rule arp table out as its MAC 
> address was unknown). And iptables does not show any forwarding rules once 
> I stop libvirtd. The NAT stays active stopping libvirtd, but I killed it 
> with iptables. Still it works. So, there must be something that switches 
> this on. I'm sure if I reboot the host the problem is back.

Yeah, I would use xenbr0 (or eth0 in 3.2 parlance) as the bridge
if you plan on using an external DHCP server and avoid the
whole NAT and dnsmasq mess. I would probably use virbr0 as a
nice virtual network only service, remove forwarding and NAT
on it and keep it for internal traffic only.


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