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Description of problem:

NetworkManager fiddles with the network interfaces in such a way that network traffic from a RHEL6 VM host is impossible.

Steps to Reproduce:
1. create a network bridge interface through virt-manager (necessary to run virtual machines that can migrate)
2. reboot the system
3. watch networking be all fucked up
  
Actual results:

Eth0 still has an IP address.  The same IP address that br0 has.

This breaks outgoing network connections and makes it impossible to do things like yum upgrade, or providing network connectivity to KVM guests.

Adding NM_CONTROLLED=no to ifcfg-eth0 results in incoming network traffic also being broken.

Additional info:

I do not believe we can ship RHEL6 in such a state that following our documentation results in a system without working networking.

Would changing the MAC address of eth0, like peth0 got a changed MAC address with Xen bridging, fix the issue?

<herbert> riel: we should fix NetworkManager, br0 and eth0 sharing the same MAC is a common setup
<herbert> with or without virt
<herbert> Xen's approach had many problems, such as incompatibilities with bonding

*** This bug has been marked as a duplicate of bug 619863 ***