QuestionQ38

Routing Policy and Manipulation

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Refer to the exhibit. Networks 172.16.31.0/24 and 172.16.30.0/24 are advertised in area 34, and network 172.22.10.0/24 is advertised in area 0. A recent security review found that users connected to routers R1 and R2 have made unauthorized access to an application running on network 172.16.31.0/24. An engineer determined that routers R1 and R2 are receiving updates for network 17.16.31.0/24. Which action resolves the issue?

  • A Apply route filtering on routers R3 and R4.
  • B Apply route filtering on routers R1 and R2.
  • C Apply route filtering on router R3 only.
  • D Apply route filtering on router R4 only.
Explanation

OSPF area prefix filtering is performed by an ABR on Type 3 summary LSAs. Both R3 and R4 border area 34 and can advertise 172.16.31.0/24 into other areas; therefore, filtering must be applied on both routers so that neither path distributes the prefix to R1 or R2.

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