CCNA Practice Exam Test Sample – Question 193

What are two benefits of using a single OSPF area network design? (Choose two.)

A. It is less CPU intensive for routers in the single area.
B. It reduces the types of LSAs that are generated.
C. It removes the need for virtual links.
D. It increases LSA response times.
E. It reduces the number of required OSPF neighbor adjacencies.

Correct Answers: B,C
Section: IP Routing Technologies

Explanation:
OSPF uses a LSDB (link state database) and fills this with LSAs (link state advertisement). The link types are as follows:

  • LSA Type 1: Router LSA
  • LSA Type 2: Network LSA
  • LSA Type 3: Summary LSA
  • LSA Type 4: Summary ASBR LSA
  • LSA Type 5: Autonomous system external LSA
  • LSA Type 6: Multicast OSPF LSA
  • LSA Type 7: Not-so-stubby area LSA
  • LSA Type 8: External attribute LSA for BGP
  • If all routers are in the same area, then many of these LSA types (Summary ASBR LSA, external LSA, etc) will not be used and will not be generated by any router.
    All areas in an Open Shortest Path First (OSPF) autonomous system must be physically connected to the backbone area (Area 0). In some cases, where this is not possible, you can use a virtual link to connect to the backbone through a non-backbone area. You can also use virtual links to connect two parts of a partitioned backbone through a nonbackbone area. The area through which you configure the virtual link, known as a transit area, must have full routing information. The transit area cannot be a stub area. Virtual links are not ideal and should really only be used for temporary network solutions or migrations. However, if all locations are in a single OSPF area this is not needed.