Which of the following descriptions about uRPF loose mode is correct? (Choose two).

Question

Options

• AIt is typically used on point-to-point interfaces where the same interface is used for both directions
• BIf a packet fails the uRPF loose mode check, the packet is then transmitted and creates a log message
• CIt is typically used on multipoint interfaces or on routers where asymmetrical routing is used (packets
• DIf a packet fails the uRPF loose mode check, the packet is then dropped

• A
  15% (8)
• B
  6% (3)
• C
  79% (41)

Explanation

When administrators use Unicast RPF in strict mode, the packet must be received on the interface that the router would use to forward the return packet. Unicast RPF configured in strict mode may drop legitimate traffic that is received on an interface that was not the router's choice for sending return traffic. Dropping this legitimate traffic could occur when asymmetric routing paths are present in the network. When administrators use Unicast RPF in loose mode, the source address must appear in the Administrators can change this behavior using the allow-default option, which allows the use of the default route in the source verification process. Additionally, a packet that contains a source address for which the return route points to the Null 0 interface will be dropped. An access list may also be specified that permits or denies certain source addresses in Unicast RPF loose mode. Care must be taken to ensure that the appropriate Unicast RPF mode (loose or strict) is configured during the deployment of this feature because it can drop legitimate traffic. Although asymmetric traffic flows may be of concern when deploying this feature, Unicast RPF loose mode is a scalable option for networks that contain asymmetric routing paths.

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