In OSPF, what type of router connects an area to the backbone and maintains routing information for each area?

• A. Internal Router
• B. ASBR
• C. Backbone Router
• D. Area Border Router

Answer: (D)

In OSPF, the router that sits at the boundary between an area and the backbone and holds routing information for each connected area is the Area Border Router. This device links non-backbone areas to the backbone (Area 0) and keeps separate link-state databases for the backbone and for every area it borders. Because of this, it can exchange routing information between areas and summarize or propagate routes across the hierarchy using inter-area routing. This specialization distinguishes it from an internal router, which lives entirely within a single area, and from an ASBR, which handles redistribution of external routes into OSPF. The concept of a distinct “backbone router” isn’t a standard term in the same way, whereas the Area Border Router precisely describes a router that connects an area to the backbone and maintains per-area routing data.