Refer to the exhibit. In this network, what will be the impact at R4 if the link between R1 and R2 fails?

Question

Exhibit

Options

• AR3 will generate a new summary (type 3) LSA when the link between R1 and R2 fails. When
• BR4 will not receive any new LSAs of any type, nor will it run SPF.
• CR4 will receive a router (type 1) LSA from R2, since it has lost its connection to R2. When R4
• DR2 will generate a new network (type 2) LSA, since it has lost its connection to 10.1.1.4/30.

• A
  9% (5)
• B
  53% (31)
• C
  26% (15)
• D
  12% (7)

Explanation

This question tests understanding of OSPF area types and LSA propagation boundaries. Based on the network topology in the exhibit, R4 resides in a totally stubby area. In a totally stubby area, the ABR blocks Type 3 (Summary), Type 4 (ASBR Summary), and Type 5 (AS External) LSAs from entering the area, sending only a single default route Type 3 LSA instead. When the link between R1 and R2 fails, new Type 1 or Type 2 LSAs are generated within the backbone (Area 0), but these intra-area LSAs for Area 0 never propagate into R4's stub area. Since the ABR's summary or default route to R4's area does not change as a result of this specific link failure, R4 receives no new LSAs of any type and therefore has no trigger to run the SPF algorithm - its routing table remains unchanged.

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