Which of the following statements regarding OSPF special areas is false?

Which of the following statements regarding OSPF special areas is false?

• A. A totally stub area allows AS external routes
• B. Different from a totally stub area, a stub area allows inter-area routes
• C. An NSSA area allows importing AS external routes
• D. A totally stub area does not allow inter-area routes

Answer: (C)

A totally stub area is designed to minimize the amount of routing information that routers have to maintain. It does this by allowing only a limited set of routes, specifically interior gateway protocol (IGP) routes from the area itself and a default route. This makes option A incorrect, as a totally stub area does not permit AS external (external) routes; it only has access to default routes for reaching external networks. When looking at option B, it accurately describes a stub area, which indeed allows inter-area routes. In contrast to a totally stub area, a stub area retains certain routes that provide connectivity for inter-area traffic, making this statement true. Choosing option C, "An NSSA area allows importing AS external routes," is where the confusion arises. In fact, a Not-So-Stubby Area (NSSA) allows the introduction of external AS routes into the area but does so using a special mechanism to allow these external routes in a controlled manner. Option D correctly states that a totally stub area does not permit inter-area routes, reinforcing why it's a defining characteristic of this type of area in OSPF. In summary, the accurate understanding is that NSSA areas are structured to manage external routes specially, but the notion here is mis

A totally stub area is designed to minimize the amount of routing information that routers have to maintain. It does this by allowing only a limited set of routes, specifically interior gateway protocol (IGP) routes from the area itself and a default route. This makes option A incorrect, as a totally stub area does not permit AS external (external) routes; it only has access to default routes for reaching external networks.

When looking at option B, it accurately describes a stub area, which indeed allows inter-area routes. In contrast to a totally stub area, a stub area retains certain routes that provide connectivity for inter-area traffic, making this statement true.

Choosing option C, "An NSSA area allows importing AS external routes," is where the confusion arises. In fact, a Not-So-Stubby Area (NSSA) allows the introduction of external AS routes into the area but does so using a special mechanism to allow these external routes in a controlled manner.

Option D correctly states that a totally stub area does not permit inter-area routes, reinforcing why it's a defining characteristic of this type of area in OSPF.

In summary, the accurate understanding is that NSSA areas are structured to manage external routes specially, but the notion here is mis