[libvirt-users] (no subject)

Justin Clift jclift at redhat.com
Tue Nov 16 17:57:19 UTC 2010

On 17/11/2010, at 3:51 AM, David M. Barlieb wrote:
> HI, I’ve just begun using libvirt as part of my KVM installation and have been having some confusion regarding networking of my virtual guests. I’m not sure if I should even be sending this to this mailing list and if not please let me know and if possible where I should be sending this inquiry.
> I understand I can setup a dedicated bridged interface for my guest. But as for the virbr interface which is the default, I’m a little confused about. When using this, does the guest os use the same ip as the host? If so, then how to packets get to the guest instead of the host. I would guess there’s an alternate mac address for the guest interface and this is how it gets there but am not certain. Sorry if this seems like a simple question but I’m not very well versed in networking.

Hi Dave,

The "default" virtual network that libvirt comes with, has NAT done to it.  So, the guests connected through it can get to the outside world, and they get reply packets... but their IP addresses aren't directly visible.

Exact same principle as (often) used in home networks these days, where the computers in a person's home have NAT applied to them by their ADSL router.

Does that help?

By the way, there's documentation around this subject being worked upon here:


It's very much "work in progress", and that won't be it's final URL.  But... it might help anyway. :)

(feel free to ask further questions and stuff in regards to that doc.  Feedback on the way through is useful. :> )

Regards and best wishes,

Justin Clift

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