Cisco Certified Network Associate (CCNA) Practice Exam

What is the distinction for routes denoted as (O*N#) in OSPF?

1. Routes to internal networks

2. Routes to external networks within NSSA

3. External summary routes

4. Default routes

The correct answer is: Routes to external networks within NSSA

Routes denoted as (O*N#) in OSPF signify external routes that are imported into an OSPF area from an external routing protocol specifically within a Not So Stubby Area (NSSA). NSSA is a special type of OSPF area that allows for external routing information to be advertised while preventing certain OSPF routers from receiving Type 5 LSA, which are used to advertise external routes. In the context of OSPF, external routes can originate from other routing protocols, such as EIGRP or BGP. When those routes are imported into OSPF within an NSSA, they are treated differently than regular internal OSPF routes. The notation (O*N#) signifies that the routes are OSPF external routes, specifically designed for areas that allow such conditions, matching the unique characteristics of NSSA. Other options do not accurately represent the meaning of (O*N#). Internal networks would be represented simply under OSPF without any external attributes. External summary routes are denoted differently and do not specifically include the NSSA context. Default routes are also a different classification in OSPF and are configured as such without the external routing protocols' context. Thus, the notation (O*N#