Comments on Virtualization With KVM On A CentOS 6.4 Server

 I had SELinux disabled on my CentOS 6.4 system. I didn't test with SELinux on; it might work, but if not, you better switch off SELinux as well:

 This is poor advice.  If you are running KVM chances are you are also going to be running a webserver of some kind, likely connected to a public network in some way.  In this setting you don't want your processes running unconstrained on the system.

 Instead of disabling SELinux entirely - set it to 'Permissive'.  This won't enforce any policies.  It will however log any process that violates the policies, so you can refer to it later and adjust your settings as necessary.

I have followed the instructions upto starting the network service.

when I run /etc/init.d/network restart I get the following error:

Shutting down interface eth0:  Device state: 3 (disconnected)
                                                           [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:  Error: Connection activation failed: Master connection not found or invalid
                                                           [FAILED]
Bringing up interface br0:  Error: Connection activation failed: Failed to determine connection's virtual interface name
                                                           [FAILED]
 

I usually just set NM_CONTROLLED=NO and then do a 'service network restart'.

I faced the same problem but now I got the solution. 

When changing the config of eth0 interface, leave it as is instead of commenting ipaddr, gateway etc etc. 

I experienced the same problem.  Where you able to resolve it?

Red Hat Enterprise Linux ~ Virtualization Guide

10.2. Bridged networking with libvirt

Bridged networking (also known as physical device sharing) is used for dedicating a physical device to a virtual machine. Bridging is often used for more advanced setups and on servers with multiple network interfaces.

Disable Xen network scripts

If your system was using a Xen bridge, it is recommended to disable the default Xen network bridge by editing /etc/xen/xend-config.sxp and changing the line:

(network-script network-bridge)

To:

(network-script /bin/true)

Disable NetworkManager

NetworkManager does not support bridging. Running NetworkManager will overwrite any manual bridge configuration. Because of this, NetworkManager should be disabled in order to use networking via the network scripts (located in the /etc/sysconfig/network-scripts/ directory):

# chkconfig NetworkManager off

# chkconfig network on

# service NetworkManager stop

# service network start

Note

As an alternative to turning off NetworkManager, add "NM_CONTROLLED=no" to the ifcfg-* scripts used in the examples.

If you do not either set this parameter or disable NetworkManager entirely, any bridge configuration will be overwritten and lost when NetworkManager next starts.

...

Thanks for the tip. I received the "Master connection not found or invalid" error when starting etho0 and br0. After setting NM_CONTROLLED=no in both the eth0 and br0 config files, that error was fixed.

A lot thanks for this kind of documents share clearly. Its never easy for me to install centOS KVM as a beginners. This post really helped me a lot. :)

Is the new version of Update Rollup 4 for virtual machine management 2012 R2 released yet? (pulled back in late October).

If possible please provide info about webvirtmgr kvm server?

Your bridge instructions are very confusing.  I used instead the much simpler

virsh iface-bridge eth0 br0