Refer to the exhibit. An engineer must create a configuration that prevents R3 from receiving the LSA about 172.16.1.4/32. Which configuration set achieves this goal? A. B. C. D.

Question

Exhibits

Options

• AOn R3 ip access-list standard R4_L0 deny host 172.16.1.4 permit any router ospf 200 distribute-list R4_L0 in
• BOn R3 ip prefix-list INTO-AREA1 seq 5 deny 172.16.1.4/32 ip prefix-list INTO-AREA1 seq 10 permit 0.0.0.0/0 le 32 router ospf 200 area 1 filter-list prefix INTO-AREA1 in
• COn R1 ip prefix-list INTO-AREA1 seq 5 deny 172.16.1.4/32 ip prefix-list INTO-AREA1 seq 10 permit 0.0.0.0/0 le 32 router ospf 200 area 1 filter-list prefix INTO-AREA1 in
• DOn R1 ip prefix-list INTO-AREA1 seq 5 deny 172.16.1.4/32 ip prefix-list INTO-AREA1 seq 10 permit 0.0.0.0/0 le 32 router ospf 200 area 1 filter-list prefix INTO-AREA1 out

• A
  3% (1)
• B
  11% (4)
• C
  84% (32)
• D
  3% (1)

Explanation

Option C is correct because R1 is the ABR (Area Border Router) connecting Area 0 and Area 1 - only ABRs generate Type 3 Summary LSAs, so the prefix filter must be applied there, not on internal routers like R3. Using area 1 filter-list prefix INTO-AREA1 in on R1 blocks the Type 3 LSA from ever being flooded into Area 1, meaning R3 never receives it at all.

Why the distractors fail:

• A is wrong because distribute-list in on R3 only filters prefixes from being installed in the routing table - the LSA still propagates into the LSDB, so R3 does receive it, violating the requirement.
• B is wrong because area 1 filter-list has no effect on an internal router like R3; this command is only meaningful on an ABR.
• D is wrong because out filters LSAs leaving Area 1 (going toward Area 0), not entering it - the direction is reversed.

Memory tip: Think of in/out relative to the area, not the router interface - area 1 filter-list in = block traffic flowing into Area 1. And always ask: "Is this router an ABR?" - if not, area filter-list is useless there.

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