what does it mean "virtual links between the VMs that have been assigned to different data centers should be embedded in the backbone network.? How we can embed a virtual link in a physcal link in the backbone network.?
All ABRs must have either direct or indirect link to the backbone area. In some cases, where it is not possible to be connected physically to the backbone area, the ABR can configure a virtual link to another router (which has a physical connection to the area backbone) within the same area.The area through which you configure the virtual link, known as a transit area, two parameters must be defined for all virtual links: transit area ID and neighbor router IP address.
A virtual link is not a physical link. It is a logical link using the least cost path between the ABR of the non-backbone connected area and the backbone ABR of the transit area. A virtual adjacency across the virtual link is formed, and routing information is exchanged.
physical link
(1) An electronic connection between two devices
(2) In data management, a pointer in an index or record that refers to the physical location of data in another file.
Virtual links can be configured between any two routers that have an interface to a single common non-backbone area. The common non-backbone area is known as the transit area.Where as,a virtual link is not a physical link. It is a logical link using the least cost path between the ABR of the non-backbone connected area and the backbone ABR of the transit area.
I agree with the submissions here. The difference is clear as highlighted by the various submissions. However, Cisco IoS allows you to configure logical virtual link into physical interface (serial WAN) in the backbone network.