Cisco Certified Network Associate (CCNA) Practice Exam

Which LSA type is not transited by ABR/ASBR into other areas?

1. Type 1: Router LSA

2. Type 2: Network LSA

3. Type 7: NSSA External LSA

4. Type 5: External LSA

The correct answer is: Type 7: NSSA External LSA

The correct choice indicates that Type 7: NSSA External LSA is not transited by ABR (Area Border Router) or ASBR (Autonomous System Boundary Router) into other areas. NSSA (Not-So-Stubby Area) is a special type of OSPF area that allows the import of external routes while also restricting certain types of routing updates. Type 7 LSAs are specifically designed for NSSAs, and they serve to carry external route information into these areas. However, when these LSAs need to be flooded into other areas, they are translated into Type 5 External LSAs by the ABR, which then allows routes to propagate outside the NSSA. Thus, the Type 7 LSA doesn’t transit as-is; instead, it undergoes conversion to Type 5 for further distribution in the OSPF domain. Other LSA types, such as Type 1 (Router LSA), Type 2 (Network LSA), and Type 5 (External LSA), are designed to be advertised and transited across various areas in OSPF, as they are fundamental to OSPF's routing operations and structure. This specification for Type 7 makes it unique in its behavior within