Your using Proxmox 3 on an OVH Server and you want to upgrade to Proxmox 4. You have a pretty simple setup and figure it will be a simple process. While this is mostly true, if you are used to just assigning one of your Failover IP’s to a container via the Proxmox interface you will quite surprised when that no longer works.
So whats the problem? LXC does not work the same way (as far as I can tell) when it comes to the network. I was forced to manually configure the network in each machine.