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JN0-102 · Question #112

What is the purpose of unicast reverse path forwarding?

The correct answer is A. to validate packet receipt on interfaces where the traffic should be received. Unicast Reverse Path Forwarding (uRPF) is a security feature that validates the source IP address of incoming packets by checking if the packet arrived on the interface that represents the best reverse path back to that source.

Routing Policy and Firewall Filters

Question

What is the purpose of unicast reverse path forwarding?

Options

  • Ato validate packet receipt on interfaces where the traffic should be received
  • Bto forward packets out the interfaces where the traffic should be received
  • Cto forward packets out the interfaces where the traffic should be sent
  • Dto validate packet receipt on interfaces where the traffic should be sent

How the community answered

(25 responses)
  • A
    92% (23)
  • C
    4% (1)
  • D
    4% (1)

Why each option

Unicast Reverse Path Forwarding (uRPF) is a security feature that validates the source IP address of incoming packets by checking if the packet arrived on the interface that represents the best reverse path back to that source.

Ato validate packet receipt on interfaces where the traffic should be receivedCorrect

Unicast Reverse Path Forwarding (uRPF) performs a lookup of the packet's source IP address in the routing table. If the incoming interface is not the best reverse path to reach the source IP, the packet is considered spoofed and is dropped, thereby validating packet receipt.

Bto forward packets out the interfaces where the traffic should be received

uRPF is a security feature for validating incoming packets, not for forwarding packets out of any interface.

Cto forward packets out the interfaces where the traffic should be sent

uRPF is not involved in forwarding packets out of interfaces; its role is source address validation on ingress.

Dto validate packet receipt on interfaces where the traffic should be sent

uRPF validates packet receipt on interfaces where the traffic *should be received* from the source, not where traffic should be *sent* to the source (though the routing table lookup determines the path back to the source).

Concept tested: Unicast Reverse Path Forwarding (uRPF) purpose

Source: https://www.juniper.net/documentation/us/en/software/junos/routing-policy/topics/topic-map/forwarding-policy-rp-filtering.html

Topics

#uRPF#reverse path forwarding#packet validation#security

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