Re: [Xen-users] what the H is this virbr0?

[Steven <xen@xxxxxxxxxxxxxxxxxxx>]

Sadique Puthen wrote:
> Steven wrote:
> > Hi,
> >
> > I just tested in the lab the new CentOS 5.1 Xen and find out it 
> > breaks network connectivity, at least in my setup.
> > It seems it is somehow making use of the 3.1 Xen version (altought I 
> > am not sure about that) but whatever changes it introduce is not 
> > documented at the location one would expect, the obvious new thing 
> > (at least for me) is this thing I will call out of guessing a virtual 
> > bridge, when I do an ifconfig on the dom0:
> > virbr0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
> >          inet addr:192.168.122.1  Bcast:192.168.122.255
> > This seems to change everything with regard to networking. I googgled 
> > a bit and read the following links but I could not find any 
> > explanation about what it is, what it does and why it breaks my setup:
> Centos 5.1 makes networking for guests a bit easier by adding virb0 
> and implementing a natted network connection for guests. This 
> shouldn't break the networking that you had previously in Centos-5.0. 
> At least it has not broken anything on my RHEL5 system when I upgraded 
> that to RHEL-5.1
> RHEL-5.1 makes it possible for you to put guests in a private network 
> behind dom0 and nat packets to your LAN through dom0. This is the 
> preferred set up for laptops. If you create guests using virt-manager, 
> it defaults the network setup to use natting, unless you explicitly 
> select to bridge the network to xenbrx. The problem is that RHEL-5.1 
> does not enable ip forwarding by default in the kernel. So if you 
> create guests and bridge them to virbr0, the guest wouldn't be able to 
> communicate to the external networks. This can simply be solved by 
> enabling ip forwarding in Dom0.
Ok, thank you. Do you know how or where to disable it?


> --Sadique
>
> > http://wiki.xensource.com/xenwiki/XenNetworking
> > http://www.cl.cam.ac.uk/research/srg/netos/xen/readmes/user/user.html#SECTION03220000000000000000 
> >
> > Can anyone point to an official information source for this beast?
> >
> > Regards,
>
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--
Steven Dugway


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