Why do large OSPF networks use a hierarchical design? (Choose three.)

Why do large OSPF networks use a hierarchical design? (Choose three.)
A . to decrease latency by increasing bandwidth
B . to reduce routing overhead
C . to speed up convergence
D . to confine network instability to single areas of the network
E . to reduce the complexity of router configuration
F . to lower costs by replacing routers with distribution layer switches

Answer: BCD

Explanation:

OSPF implements a two-tier hierarchical routing model that uses a core or backbone tier known as area zero (0). Attached to that backbone via area border routers (ABRs) are a number of secondary tier areas. The hierarchical approach is used to achieve the following:

– Rapid convergence because of link and/or switch failures

– Deterministic traffic recovery

– Scalable and manageable routing hierarchy, reduced routing overhead.