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

[Sadique Puthen <sputhenp@xxxxxxxxxx>]

Sadique Puthen wrote:
> Steven wrote:
> > 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?
> /etc/libvirt/qemu/networks/autostart/default.xml
Sorry, I thought you want to disable virbr0.  If your question how to 
enable ip forwarding, then add "net.ipv4.ip_forward = 0" to 
/etc/sysctl.conf and run "sysctl -p".
--Sadique

> --Sadique
>
> > > --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,
> > > _______________________________________________
> > > Xen-users mailing list
> > > Xen-users@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-users
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