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Re: [Xen-users] newbie in trouble with CentOS Xen

  • To: xen-users@xxxxxxxxxxxxx
  • From: Alexandre Kouznetsov <alk@xxxxxxxxxx>
  • Date: Fri, 05 Apr 2013 10:43:45 -0600
  • Delivery-date: Fri, 05 Apr 2013 16:44:47 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

El 05/04/13 10:13, Greg Woods escribió:
On Fri, 2013-04-05 at 10:05 -0600, Alexandre Kouznetsov wrote:

It seems like, Dom0's IP connectivity is not done directly via the
actual device. Instead it creates a vif0.2 and maps it as eth2 to Dom0,
as it would do with any other Dom.
Seems much cleaner than the setup I described before, as "old ways",
when a eth was renamed to peth and a bridge called eth was created.

We're getting a bit away from the original topic,
The original topic is still discussed on another branch of this thread (:

We've got the ethX devices
which are the physical device, same as any non-Xen system,
No. While Dom0 is booted, it's virtualized. See all that vif0.X, they are interfaces exported to a Domain with ID 0.

and the
xenbrX devices, which are the actual bridges.
Right, they communicate the backend vif's with the physical network.

The pethX devices don't
seem to serve any real purpose. I would hazard a guess that the pethX
devices aren't really needed at all, and are just there for historical

Yes they do serve a purpose. ethX devices you see in your Dom0 (note, this seems to be CentOS specific Xen stuff) are not real network interfaces. They are virtualized, just like any other network interface in any other DomU. They are backed by a corresponding vif0.X device. Just as in case of DomU, vif0.X devices are bridged together with a physical interface within Dom0. That is where pethX comes into play, it links the bridge to the physical network. Also, it's used to interact with the physical card, for MTU, error correction settings, WOL, firmware, etc.

So the topology is like this:

 Dom0 eth0
physical port


Alexandre Kouznetsov

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