Boundary nodes in the Multi-area SPB network require a robust Fabric path between them in both areas (home and remote). If a robust connection for one of the areas is not possible, you can create a virtual NNI link and establish a virtual Fabric adjacency over the area with the robust connection. For instance, if an adjacency exists between two boundary nodes in the home area, you can use virtual NNI functionality to establish a Fabric adjacency in the remote area, and vice versa.
To create virtual NNI link functionality between boundary nodes, you must complete the following tasks:
IP Shortcuts automatically redistributes the IP address in the specific area without the need for an IS-IS redistribution policy. Boundary nodes receive this IP address in the corresponding area as an IS-IS redistributed route.