Cisco Certified Network Associate (CCNA) Practice Exam

What is the characteristic of a Not-So-Stubby-Area (NSSA)?

1. It permits only type 1 LSA's

2. It allows type 3 LSA's while blocking types 4 and 5

3. It permits type 1 and 2 LSA's while blocking types 3, 4, 5, and 7

4. It enables type 3 LSA containing a default route to the ABR

The correct answer is: It permits type 1 and 2 LSA's while blocking types 3, 4, 5, and 7

A Not-So-Stubby-Area (NSSA) is a specialized area in OSPF (Open Shortest Path First) routing that possesses specific characteristics regarding the types of Link State Advertisements (LSAs) it handles. The correct option accurately reflects that an NSSA permits the flooding of type 1 (router) and type 2 (network) LSAs, which are crucial for establishing intra-area communication. What sets an NSSA apart is its ability to block type 3 (summary), type 4 (ASBR-summary), and type 5 (external) LSAs while allowing type 7 LSAs. Type 7 LSAs are used specifically in NSSAs to carry external routing information, such as routes from other Autonomous Systems, but only in a way that adheres to the constraints of an NSSA. This unique characteristic is essential because it allows an NSSA to connect to other OSPF areas and external networks while preventing unnecessary flooding of external routes, thereby maintaining a more manageable routing table. The other options describe characteristics that do not accurately define how an NSSA operates. For instance, type 1 and type 2 LSAs are indeed permitted, but the blocking of type 3, 4