Virtual NNI Links for Multi-Area Boundary Nodes

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:

Configure the loopback IP address as the source IP address using the Multi-area virtual link flag.
Configure a logical IS-IS interface using the Multi-area virtual link flag.
Configure IS-IS on the logical interface.
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.

Virtual NNI Links on Boundary Nodes Considerations and Restrictions

The following list identifies considerations and restrictions that apply to virtual NNI links on boundary nodes:

Function on boundary nodes only.
Support only a CLIP (loopback) interface configured on the GRT.
Support only one CLIP (loopback) interface.
Do not support Bidirectional Forwarding Detection (BFD). You cannot enable BFD on a logical interface for a virtual NNI link.
Cannot coexist with VXLAN Gateway. You cannot enable VXLAN Gateway on a loopback interface for a virtual NNI link and you cannot create a loopback interface for a virtual NNI link when VXLAN Gateway is enabled.