300-410 ENARSI: Implementing Cisco Enterprise Advanced Routing and ServicesDemo

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QuestionQ380

Layer 3 Technologies

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Refer to the exhibit. An engineer recently implemented uRPF by configuring the ip verify unicast source reachable-via rx command on interface gi0/3. Immediately after implementing uRPF, the engineer observed that an inbound packet on the gi0/3 interface with a source address of 172.16.3.251 was dropped. Which action resolves the issue?

  • A Configure uRPF loose mode to forward the packet.
  • B Permit the 172.16.3.251 in the inbound ACL on interface gi0/3.
  • C Remove inbound ACL from the interface gi0/3 to allow 172.16.3.251.
  • D Configure uRPF strict mode to forward the packet.
Explanation

The rx keyword enables strict uRPF, which accepts a packet only when the route back to its source uses the same interface on which the packet arrived. The route for 172.16.3.251 is through GigabitEthernet0/2, not gi0/3, so strict uRPF drops the packet. Loose uRPF validates that the source is reachable through any interface and permits this routable source address.

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