View the IP Unicast FIB

Use the following procedure to display the IP unicast Forwarding Information Base (FIB). The tab shows IP routes from remote Backbone Edge Bridges (BEBs)

In SPBM, each node has a System ID, which also serves as Backbone MAC address (B-MAC) of the switch. These Backbone MAC addresses are populated into the SPBM VLAN Forwarding Information Base (FIB). When the network topology is discovered and stored in the IS-IS link-state database, each node calculates shortest path trees for each source node, so that a unicast path now exists from every node to every other node. With this information, each node populates unicast information received from SPBM into the FIB for forwarding purposes.

I-SIDs are only used for virtual services (Layer 2 VSNs and Layer 3 VSNs). If you only enable IP Shortcuts on the Backbone Edge Bridges, I-SIDs are never exchanged in the network as IP Shortcuts allows for Global Routing Table (GRT) IP networks to be transported across IS-IS.

The IP Unicast FIB tab displays all of the IS-IS routes in the IS-IS LSDB. The Preference column in the IP Unicast FIB tab displays the IP route preference.

Routes within the same VSN are added to the LSDB with a default preference of 7. Inter-VSN routes are added to the LSDB with a route preference of 200. IS-IS accept policies allow you to change the route preference for incoming routes. If the same route is learned from multiple sources with different route preferences, then the routes are not considered equal cost multipath (ECMP) routes. The route with the lowest route preference is the preferred route. In Layer 2, in the event of a tie-break between routes from multiple sources, the tie-breaking is based on cost and hop count.