networking in virtual machines using libvirt tools

[Rich Mahn]

I am trying to set up a virtual machine that has a routable IP address
on the same subnet (and physically the same ethernet card) as the host
machine, running f11 on the host.

Using virsh and related, I can easily set up the network on the VM as
a natted IP with dhcp.  This is taken care of in the defaults for
virt-manager.  I can also set up, (but not quite as easily) the
network the way I want on a CentOS/XEN host.  Unfortunately CentOS
doesn't have a number of other features that I want/need.

So...is there some XML snippet I can add to the domain that will
do what I want automatically?  Or is there a script (or maybe I need
to write one) that can be invoked to set up the interfaces?

I would certainly be appreciative to get some pointers on how to proceed.

To make what I want a little clearer:

My host has a routable IP address such as 123.45.67.89.  I want my
VM to have the routable IP address 123.45.67.90.

I realize I could probably do this with iptables on the host and using
the 192.168.x.x IP on the VM, but then the VM has an incorrect idea of
it's correct IP.

Any help is appreciated.  Thanks.

[Mark McLoughlin]

On Thu, 2009-07-23 at 15:01 -0400, Rich Mahn wrote:
> I am trying to set up a virtual machine that has a routable IP address
> on the same subnet (and physically the same ethernet card) as the host
> machine, running f11 on the host.
>
> Using virsh and related, I can easily set up the network on the VM as
> a natted IP with dhcp.  This is taken care of in the defaults for
> virt-manager.  I can also set up, (but not quite as easily) the
> network the way I want on a CentOS/XEN host.  Unfortunately CentOS
> doesn't have a number of other features that I want/need.
>
> So...is there some XML snippet I can add to the domain that will
> do what I want automatically?  Or is there a script (or maybe I need
> to write one) that can be invoked to set up the interfaces?
>
> I would certainly be appreciative to get some pointers on how to proceed.
>
> To make what I want a little clearer:
>
> My host has a routable IP address such as 123.45.67.89.  I want my
> VM to have the routable IP address 123.45.67.90.

Have you seen this?

http://wiki.libvirt.org/page/Networking#Fedora.2FRHEL_Bridging

Unless I misunderstand, all you need to do is create a bridge for the
interface in the host, connect the guest's network backend in the host
and statically configure the guest's interface with that IP address.

Cheers,
Mark.

[Rich Mahn]

> On Thu, 2009-07-23 at 15:01 -0400, Rich Mahn wrote:
> > I am trying to set up a virtual machine that has a routable IP address
> > on the same subnet (and physically the same ethernet card) as the host
> > machine, running f11 on the host.
> >
> > Using virsh and related, I can easily set up the network on the VM as
> > a natted IP with dhcp.  This is taken care of in the defaults for
> > virt-manager.  I can also set up, (but not quite as easily) the
> > network the way I want on a CentOS/XEN host.  Unfortunately CentOS
> > doesn't have a number of other features that I want/need.
> >
> > So...is there some XML snippet I can add to the domain that will
> > do what I want automatically?  Or is there a script (or maybe I need
> > to write one) that can be invoked to set up the interfaces?
> >
> > I would certainly be appreciative to get some pointers on how to proceed.
> >
> > To make what I want a little clearer:
> >
> > My host has a routable IP address such as 123.45.67.89.  I want my
> > VM to have the routable IP address 123.45.67.90.
> Have you seen this?
> http://wiki.libvirt.org/page/Networking#Fedora.2FRHEL_Bridging
> Unless I misunderstand, all you need to do is create a bridge for the
> interface in the host, connect the guest's network backend in the host
> and statically configure the guest's interface with that IP address.
> Cheers,
> Mark.

Thanks Mark.  That is exactly what I was looking for.  I'll try it out
and report back.

Rich

[Rich Mahn]

=== snip snip ===
> > Have you seen this?
> > http://wiki.libvirt.org/page/Networking#Fedora.2FRHEL_Bridging
> > Unless I misunderstand, all you need to do is create a bridge for the
> > interface in the host, connect the guest's network backend in the host
> > and statically configure the guest's interface with that IP address.
> > Cheers,
> > Mark.
> Thanks Mark.  That is exactly what I was looking for.  I'll try it out
> and report back.
> Rich

The instructions are for F9 and as such have a couple very minor
problems.  For example, I can't find lokkit for f11.  However, other
than that, I just pretty much followed the cookbook to get things
working.  I had a small problem with the networking until I noticed
that the cookbook was configured for dhcp and I use fixed IPs.  Once I
corrected for that everything worked GREAT!!!!

I looked around the site and that wiki.libvirt.org has some really
great information available.

Thanks loads.

rich