An engineer is designing an OSPF network with multiple nonbackbone areas connecled to the backbone area via a hub-and-spoke topology. Each hub-and-spoke area has a large number of spoke routers…

Question

Options

• AConfigure hub-and-spoke areas as stub.
• BUse External Type 2 metric: across the OSPF domain.
• CConfigure hub-and-spake areas as totally stubby.
• DImplement summarization on the ABR routers of hub-and-spoke areas
• EImplement summarization on the ASBR routers in the backbone area

• A
  28% (7)
• B
  8% (2)
• C
  52% (13)
• E
  12% (3)

Explanation

In an OSPF hub-and-spoke design with a large number of spoke routers, stability problems arise from excessive LSA flooding and large LSDBs. Two actions directly address this: (C) Configuring hub-and-spoke areas as totally stubby eliminates both Type 5 LSAs (external routes) and Type 3 LSAs (inter-area summaries), replacing all external and inter-area routing information with a single default route injected by the ABR. This dramatically reduces LSDB size and prevents external topology changes from destabilizing spoke areas. (D) Summarization on the ABR routers aggregates specific prefixes into fewer summary routes, limiting LSA propagation between areas and dampening the impact of individual route flaps. Together, these two measures reduce SPF recalculation frequency and contain the blast radius of topology changes.

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