Cisco Certified Network Associate (CCNA) Practice Exam

Which LSA is originated by an ASBR and lists routes redistributed into OSPF from another routing protocol?

1. Type 2 - Network LSA

2. Type 3 - Summary LSA

3. Type 5 - External LSA

4. Type 4 - ASBR Summary LSA

The correct answer is: Type 5 - External LSA

The correct answer is Type 5 - External LSA. Type 5 LSAs are specifically generated by Autonomous System Boundary Routers (ASBRs) in OSPF environments. These LSAs are used to advertise routes that have been redistributed from external routing protocols, such as EIGRP or BGP, into an OSPF domain. Essentially, this allows OSPF to have knowledge of routes that were learned from outside its own OSPF network, facilitating better routing decisions based on a mix of internal OSPF routes and those that come from other protocols. In contrast, Type 2 Network LSAs are used to represent a multi-access network and are not related to redistribution processes. Type 3 Summary LSAs serve to summarize internal OSPF routes between areas, meaning they help with inter-area routing but not with external routing. Lastly, Type 4 ASBR Summary LSAs are utilized to inform OSPF routers about the presence and location of an ASBR, but they do not contain the actual external routes themselves. Therefore, the distinctive role of the Type 5 LSA in advertising external routes makes it the correct answer.