[virt] Did you know virbr0 was not a real bridge?

[Michael DeHaan]

virbr0 as created by libvirt is a private network, it's not a real bridge.

If you want your guests to be reachable, you need to create a real 
bridge on your virtual hosts and use that as the --virt-bridge in Cobbler.

Instructions are here:

https://fedorahosted.org/cobbler/wiki/VirtNetworkingSetupForUseWithKoan

Making a snippet that automatically makes a bridge for the first 
interface seems like a nice thing to do (or finding some way to do this 
with interface objects).

--Michael

[James Cammarata]

On Thu, 26 Mar 2009 15:59:08 -0400, Michael DeHaan 
wrote:
> virbr0 as created by libvirt is a private network, it's not a real

bridge.
> If you want your guests to be reachable, you need to create a real 
> bridge on your virtual hosts and use that as the --virt-bridge in

Cobbler.
> Instructions are here:
>
> https://fedorahosted.org/cobbler/wiki/VirtNetworkingSetupForUseWithKoan
>
> Making a snippet that automatically makes a bridge for the first 
> interface seems like a nice thing to do (or finding some way to do this 
> with interface objects).
>
> --Michael

FWIW, I run xen on RHEL5.2 and this is all pretty much setup for you there.
 The networking scripts handle the creation of the "bridge" for you, but I
believe it is still up to you to setup the sysctl/iptables correctly so
that natting/forwarding work.  It's been a few months since I got it setup
though, so I forget if I had to do any voodoo, but I have my vm's hiding
quietly behind a private network here at work (the desktop team does not
appreciate rogue dhcp servers breaking things...)

[Michael DeHaan]

James Cammarata wrote:
> On Thu, 26 Mar 2009 15:59:08 -0400, Michael DeHaan 
> wrote:
> > virbr0 as created by libvirt is a private network, it's not a real
>
> bridge.
> > If you want your guests to be reachable, you need to create a real 
> > bridge on your virtual hosts and use that as the --virt-bridge in
>
> Cobbler.
> > Instructions are here:
> >
> > https://fedorahosted.org/cobbler/wiki/VirtNetworkingSetupForUseWithKoan
> >
> > Making a snippet that automatically makes a bridge for the first 
> > interface seems like a nice thing to do (or finding some way to do this 
> > with interface objects).
> >
> > --Michael
>
> FWIW, I run xen on RHEL5.2 and this is all pretty much setup for you there.
>  The networking scripts handle the creation of the "bridge" for you, but I
> believe it is still up to you to setup the sysctl/iptables correctly so
> that natting/forwarding work.  It's been a few months since I got it setup
> though, so I forget if I had to do any voodoo, but I have my vm's hiding
> quietly behind a private network here at work (the desktop team does not
> appreciate rogue dhcp servers breaking things...)

Yes,

xenbr0 is a real bridge.

If you have that, using xenbr0 is fine.  I'll update the docs to make 
that clearer.

--Michael

[James Cammarata]

On Thu, 26 Mar 2009 16:08:43 -0400, Michael DeHaan 
wrote:
> James Cammarata wrote:
> > On Thu, 26 Mar 2009 15:59:08 -0400, Michael DeHaan 
> > wrote:
> > > virbr0 as created by libvirt is a private network, it's not a real
> >
> > bridge.
> > > If you want your guests to be reachable, you need to create a real 
> > > bridge on your virtual hosts and use that as the --virt-bridge in
> >
> > Cobbler.
> > > Instructions are here:
> > >
> > > https://fedorahosted.org/cobbler/wiki/VirtNetworkingSetupForUseWithKoan
> > >
> > > Making a snippet that automatically makes a bridge for the first 
> > > interface seems like a nice thing to do (or finding some way to do this
> > > with interface objects).
> > >
> > > --Michael
> >
> > FWIW, I run xen on RHEL5.2 and this is all pretty much setup for you
> > there.
> >  The networking scripts handle the creation of the "bridge" for you, but
> >  I
> > believe it is still up to you to setup the sysctl/iptables correctly so
> > that natting/forwarding work.  It's been a few months since I got it
> > setup
> > though, so I forget if I had to do any voodoo, but I have my vm's hiding
> > quietly behind a private network here at work (the desktop team does not
> > appreciate rogue dhcp servers breaking things...)
>
> Yes,
>
> xenbr0 is a real bridge.
>
> If you have that, using xenbr0 is fine.  I'll update the docs to make 
> that clearer.
>
> --Michael

No, I'm using virbr0 on mine.

[Mykel Alvis]

Thanks for the instructions! I have a lot to learn about bridged networking,
and my problem doing this shows it.

I have followed the instructions on the wiki, creating an ifcfg-peth0 and
changing ifcfg-etho to the specified content.  When I restart the network, I
get

Device peth0 does not seem to be present, delaying initialization. [FAILED]
 followed by
Device eth0 already exists; can't create bridge with the same name [FAILED]

Any suggestions about how I've failed to do this properly?

[Michael DeHaan]

Mykel Alvis wrote:
> Thanks for the instructions! I have a lot to learn about bridged 
> networking, and my problem doing this shows it.
>
> I have followed the instructions on the wiki, creating an ifcfg-peth0 
> and changing ifcfg-etho to the specified content.  When I restart the 
> network, I get
>
> Device peth0 does not seem to be present, delaying initialization. 
> [FAILED]
>  followed by
> Device eth0 already exists; can't create bridge with the same name 
> [FAILED]
>
> Any suggestions about how I've failed to do this properly?
>
> cobbler mailing list
> [e-mail]
> https://fedorahosted.org/mailman/listinfo/cobbler

Sounds like your network config files are probably incorrect somehow, 
but it's hard to say.    Could you paste both and let us look at them?

For Fedora, I also put NM_CONTROLLED=no in each of them now to make sure 
Network Manager doesn't try to manage them, and/or end up disabling
Network Manager.

(I've also noted if the scripts aren't named ifcfg.*[d]*, the service 
script won't always start them, but you wouldn't have that problem with 
the above names).

--Michael