PCI slot assignment
On the KVM platform, when hot-plugging a network interface into a vRouter, unless you explicitly specify the PCI slot address, the router plugs the interface into the next available PCI slot with the higher slot number.
If the first and third slots are in use, and a new interface is introduced, the new interface will take the next available PCI slot with the higher slot number. In this case, it will take PCI slot-4 and not PCI slot-2. The reason is that slot-2 is unavailable because it was previously used after the system was booted.