Cisco Certified Network Associate (CCNA) Practice Exam

Which LSA type is allowed in an OSPF Totally NSSA?

1. Only type 3 LSA's

2. Only type 1 and 2 LSA's

3. Type 5 LSA's

4. Types 1, 2, and 7 LSA's

The correct answer is: Types 1, 2, and 7 LSA's

In an OSPF Totally Not-So-Stubby Area (Totally NSSA), the types of Link-State Advertisements (LSAs) that are allowed include Type 1, Type 2, and Type 7 LSAs. Type 1 LSAs represent router information and are generated by each router in the area. They provide details about the router's interfaces and their relationships to other routers. Type 2 LSAs indicate the existence of multi-access networks and represent the network itself, including information about the routers attached to that network. Type 7 LSAs are unique to NSSAs and are used to carry external routing information into the area. Instead of using Type 5 LSAs, which carry external routing information in standard areas, NSSAs utilize Type 7 LSAs to provide this capability while still maintaining the area as a stub. In this configuration, Type 7 LSAs can be translated into Type 5 LSAs when they leave the NSSA. Thus, the combination of Types 1, 2, and 7 LSAs allows for a robust routing scenario that accommodates external routes within a Totally NSSA but also keeps the minimal routing information typically associated with stub areas.