[CentOS-virt] Finally switching from Xen to KVM - question about networking

Tue Jun 10 16:05:34 UTC 2014
Digimer <lists at alteeve.ca>

On 10/06/14 11:46 AM, Steve Campbell wrote:
> On 6/10/2014 10:46 AM, Digimer wrote:
>> On 10/06/14 10:03 AM, Steve Campbell wrote:
>>> I had so much trouble putting Centos 6 guest VMs on a Centos 5 host that
>>> I finally switched to a Centos 6 host.
>>> I've not needed more that test VMs, so I've used Virtual Machine Manager
>>> on the old system, which worked pretty well, so I decided to create my
>>> first KVM guest machine. I noticed when I created it, I only had the
>>> options of NAT for my network interface, so I used that (obvious).
>>> Well, after starting the VM, I find I don't have connectivity with that
>>> interface. Reading, I find examples where I need to create bridges
>>> perhaps. Xen did most of this for me, so it's a little new to me.
>>> Can anyone throw me a clue, please?
>>> steve campbell
>> Setting up a bridge is not that hard, and it will give your VMs direct
>> access to the outside world, and host <-> VM access just fine as well.
>> Here is a link showing how to setup a bridge connected to a bond
>> device. Ignore the bond and pretend it is a straight ethX device:
>> https://alteeve.ca/w/AN!Cluster_Tutorial_2#Configuring_our_Bridge.2C_Bonds_and_Interfaces
> The host has a device named virbr0 that is installed during system
> installation. It also has a network device vnet0. There are no files in
> /etc/sysconfig/network-scripts for these.
> Shouldn't I be able to use the virbr0 virtual bridge for this? I've
> tried setting up the VM's device with all of the options that is listed,
> but to no avail.
> Should I need to set up another bridge for this?
> And thanks for the link.
> steve

virbr0 is created and managed by libvirtd. If you open Virtual Machine 
Manager, connect to localhost and then double-click on 'localhost', you 
will see a tab for creating/managing bridges (NAT'ed, generally). I 
disable 'virbr0' as NAT'ing is generally not what I want.

The 'vnetX' devices are dynamically created to link a VM's interface to 
a bridge. Think of them as virtual network cables. They get created and 
destroyed as needed.

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