This interior gateway routing protocol uses hierarchical areas with Area 0 as the backbone area.

• A. BGP
• B. RIP
• C. OSPF
• D. EIGRP

Answer: (C)

Hierarchical routing with a central backbone is a hallmark of this protocol. In this design, the network is divided into areas, and a special backbone area serves as the core that all other areas must connect to. Each area builds its own link-state database and runs its own SPF calculation, which keeps routing decisions localized and scalable. Inter-area routing can only happen through the backbone, with Area Border Routers bridging non-backbone areas to it. This structure allows the protocol to scale to large networks while preserving fast convergence and efficient routing.

Other protocols don’t follow this backbone-area model. The first focuses on routing between different autonomous systems and isn’t designed around a central backbone of areas. The second is a basic distance-vector protocol without area segmentation, offering limited scalability. The last is a Cisco-proprietary protocol that uses its own routing philosophy and doesn’t employ the Area 0 backbone concept.