In an OSPF network, which area distributes routing information between areas and consists of all area border routers, networks not wholly contained in any area, and their attached routers?

• A. Backbone
• B. Area 0
• C. Internal Area
• D. Transit Area

Answer: (A)

In OSPF, inter-area routing hinges on the backbone area, Area 0, which acts as the central hub for all routes between different areas. This backbone is where area border routers connect to each other and to networks that aren’t contained within a single area, and from which summary routing information is distributed to other areas. Because all inter-area traffic must pass through this central area, every non-backbone area relies on Area 0 to reach destinations in other areas, with ABRs linking those areas to the backbone. If the backbone isn’t physically contiguous, virtual links can be used to maintain that connectivity, but the backbone remains the core structure that distributes routing information between areas. Therefore, the best answer is the backbone (Area 0).