[Users] veth and bridge mac address

[Roman Haefeli]

Hi all

We're still using OpenVZ kernels from the Proxmox project (which are -
from what I know - based on the rpm packages provided by the OpenVZ
team) in our produciton environment while testing the kernels provided
by download.openvz.org.

I found a small difference in bridging behavior, which might have severe
effects. When starting a CT configured to use VETH virtual network
interface, the virtual interface is attached to the bridge configured on
the HN. When running 042stab085.20 on the HN, the MAC address of the
bridge is always the one of the interface with the smallest MAC address.
If the CT's VETH MAC is smaller than the MAC of the NIC of the HN, the
bridge's MAC changes whenever the CT is started or stopped. This can
lead to temporary network outages (up to half a minute) on that bridge. 

The behaviour of the latest proxmox kernel (pve-kernel-2.6.32-26-pve) -
which is based on  042stab081.3 - is different. The bridge MAC is the
one of the physical NIC at any time, no matter what MAC addresses the
CTs are using. 

Any problems related to MAC address switching on the HN bridge are
easily mitigated by making sure that all CTs are using a high enough MAC
address. However, a kernel with the behaviour of the proxmox kernel is
desirable, IMHO.

Roman