Which of the following descriptions of OSPF's own anti-environment measures are correct? (Multiple choice)

Question

Options

• AASBR is not allowed to exist in the OSPF backbone area
• BWhen OSPF divides areas, it stipulates that all non-backbone areas must be directly connected to the backbone area, and communications between non-backbone areas must be forwarded by the backbone area.
• COSPF's LSA flooding has a maximum of 16 hops. If it exceeds 16 hops, the LSA will be discarded.
• DOnly one ABR is allowed between the OSPF backbone area and the non-backbone area.
• ERouters in the same area calculate a loop-free shortest path tree with itself as the root based on LSDB.

• A
  3% (1)
• B
  78% (28)
• C
  11% (4)
• D
  8% (3)

Explanation

B is correct because OSPF's hierarchical design mandates that all non-backbone areas (non-Area 0) must connect directly to the backbone area (Area 0), and all inter-area traffic must transit through it - this topology constraint is a core loop-prevention mechanism. E is correct because every router within an area holds an identical LSDB and independently runs Dijkstra's SPF algorithm rooted at itself, which mathematically guarantees a loop-free shortest path tree within that area.

A is wrong - ASBRs can exist in any OSPF area, including Area 0; it is stub areas that prohibit ASBRs (because stub areas block external LSAs). C is wrong - the 16-hop limit belongs to RIP, not OSPF; OSPF is link-state and has no hop-count limit, instead using area boundaries to control LSA flooding scope. D is wrong - multiple ABRs between a non-backbone area and Area 0 are not only allowed but recommended for redundancy.

Memory tip: Think of OSPF as a "hub-and-spoke airport" - Area 0 is the hub, all other areas are spokes, and every connecting flight (inter-area traffic) must go through the hub. The "16 hops = death" rule is RIP's problem, not OSPF's.

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