Cisco Certified Network Associate (CCNA) Practice Exam

An external LSA is represented by what in the OSPF routing table?

1. (O*E)

2. (O*N)

3. (O*E#)

4. (O*IA)

The correct answer is: (O*E#)

In the OSPF routing table, an external LSA (Link-State Advertisement) is indicated by the notation (O*E#). This representation means that the route being referred to is an external route learned from another OSPF area or an external protocol, such as BGP. The "O" signifies that the route is OSPF-learned, the asterisk (*) indicates that it is a best or primary route, and the "E#" signifies that it is an external route, with the `#` character indicating that the route is type E1 or E2. Understanding this notation is essential for network professionals because it helps differentiate between internal OSPF routes, external routes from other OSPF areas, and routes learned from other protocols altogether. Other notations like (O*N) or (O*IA) relate to internal OSPF routes or inter-area routes, respectively, but do not apply to external LSAs, which is why (O*E#) is the only correct representation for external LSAs in the OSPF routing table.