Which statement about Area 0 in OSPF is true?

• A. A virtual area used for testing
• B. An area for external routes only
• C. An area used for distributing VRRP
• D. The backbone region of an OSPF-enabled network

Answer: (D)

Area 0 is the backbone of an OSPF network; it acts as the central hub that all other areas connect through. Inter-area routing information must pass through this backbone, and every area must have a path to Area 0—directly or via a virtual link—to enable routing between areas. That's why Area 0 is described as the backbone region of an OSPF-enabled network. The other descriptions don’t match how OSPF areas are used: there isn’t a designated testing area, it’s not restricted to external routes only, and VRRP distribution is a separate protocol function rather than a property of an OSPF area.