Cisco Certified Network Associate (CCNA) Practice Exam

Which LSA originated by the ABR contains external routes redistributed throughout the network?

1. Type 1 - Router LSA

2. Type 3 - Summary LSA

3. Type 4 - ASBR Summary LSA

4. Type 5 - External LSA

The correct answer is: Type 4 - ASBR Summary LSA

The correct choice is based on the role of the ABR (Area Border Router) in OSPF (Open Shortest Path First) routing. The ABR is responsible for connecting different OSPF areas and managing the distribution of routing information between these areas. In the context of OSPF, the Type 4 LSA, also known as the ASBR Summary LSA, is specifically used by an ABR to advertise the presence of an ASBR (Autonomous System Boundary Router). This type of LSA provides information about how to reach external routes that have been redistributed into OSPF from other routing protocols, such as BGP or EIGRP. It essentially informs other OSPF areas about an ASBR and its external routes, but does not contain the detailed external route information itself. In contrast, the Type 5 LSA conveys the actual external routing information that is redistributed by the ASBR into OSPF, but it is not specifically originated by the ABR. Type 1 LSAs represent router-to-router link state information and are not concerned with external routes. Type 3 LSAs, known as Summary LSAs, are also originated by ABRs but are used to summarize internal OSPF routes