The designated boundary node in the Multi-area SPB network creates the area virtual node. The area virtual node sums up an entire network topology in a single virtual node representing all the services from the represented area.
When considering the shortest path between two nodes in different areas in the Multi-area SPB network, the area virtual node logically connects the shortest path within one area to the shortest path within another area. The area virtual nodes help the Multi-area SPB network to visualize any external area as a single IS-IS entity.
The boundary nodes in the Multi-area SPB network exposes one virtual node in each of two connected areas, to represent a collection of nodes from the other area. On the basis of the policies that you configure on the boundary nodes, you can control the services that the system exports from a home area to the remote area as the system includes the configuration in the Link State Packets (LSP) of the corresponding area virtual node.
You can configure the area virtual node parameters on both home and remote IS-IS instances. For more information about configuring the area virtual node, see Configure IS-IS Multi-area SPB Virtual Node.