Refer to the exhibit. A network engineer applied configuration on R5 to summarize all OSPF routes, but R4 is still receiving specific routes from R5. The engineer has confirmed that both R5 and R4 rou

Question

Exhibit

Options

• ARemove summarization configuration on R5 and configure it on R4
• BConfigure a sham link between R4 and R5 to support summarization within Area 2
• CMove R4 and R5 in separate areas as now they maintain the same link-state database
• DClear link-state database on both R4 and R5 routers for summarization to work

• A
  4% (2)
• B
  17% (8)
• C
  72% (34)
• D
  6% (3)

Explanation

OSPF inter-area summarization can only be performed by an ABR (Area Border Router) - a router that sits on the boundary between two different areas. If R4 and R5 are both in Area 2, they share the same link-state database and neither qualifies as an ABR, so the area range summarization command has no effect regardless of correct syntax. Moving them into separate areas makes R5 an ABR with a real area boundary to summarize across, which is the only way summarization can function in OSPF.

Why the distractors are wrong:

• A - Moving the config to R4 doesn't help; the same-area constraint applies to R4 equally. The problem is topology, not which router holds the config.
• B - Sham links are an MPLS/VPN OSPF feature used to prevent backdoor paths from overriding VPN routes; they have no role in enabling summarization.
• D - Clearing the LSDB is a temporary operational action that won't change the fundamental architecture. The routers will re-sync to the same database and summarization will still fail.

Memory tip: Think "ABR = summarization gatekeeper." OSPF summarization only fires when a router is advertising routes between areas. No area boundary = no summary. If summarization isn't working, ask: "Is this router actually an ABR?"

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