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Re: [Xen-users] Is # of VMs per physical host limited by bridging?

On Thu, 2006-03-30 at 22:00 -0500, Amitayu Das wrote:
> I've got a quick question.
> http://wiki.xensource.com/xenwiki/XenNetworking
> says that Xen creates, by default, eight pair of "connected virtual
> ethernet
> interfaces" for use by dom0. Does this mean that
> a. If we're using bridging, # of VMs are limited to 8 per physical
> host (leaving Dom0)? or this has got nothing to do with the # of VMs
> running in a physical host?

They have nothing to do with the number of VMs you can run.

The eight "virtual ethernet cables" (veth# and vif 0.#) that xen creates
at boot time are not used for dom0 to connect to VMs.  They exist for
use by dom0 to connect to up to eight internal bridges (virtual ethernet

As each VM is started, xen dynamically creates one or more NEW virtual
ethernet cables between that VM and dom0 (eth0 on the VM, vif#.0 on
dom0), and attaches it to a bridge, which you control in the domU's
config file vif= statement.

I believe you should start out with the simplest config, using
'network-bridge', which creates one bridge, and attaches the dom0's eth0
physical network interface and all the VMs (including dom0) to that
bridge.  Once you are more comfortable with how it works, then you can
try a more complex configuration, if you need to.

Patrick Wolfe  (pwolfe@xxxxxxxxxxxxxx)

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