Allow us to control IP/DNS settings for VMs which are added to a Virtual Network
Currently, private IP addresses are assigned in the order that you create VMs. For some more complex scenarios such as AD, this adds an extra planning step. It also makes it difficult to replace VMs which have a knows static address.
Pre-defined IP addresses for VMs within Virtual Network will be released shortly.
DNS Settings can be specified at the VNet level or overridden at the VM level even today.
Jesus Salas commented
Hi Narayan. When VMs are restarted due Azure Maintenance or a VM reboot the Network Interface seems regenerated (has a new X for 'Network Interface X' and any custom DNS Settings are cleared out by this process.