Which of the following descriptions about uRPF loose mode is correct? (Choose two).
A.
It is typically used on point-to-point interfaces where the same interface is used for both
directions of packet flows; if the source address has a return route in the FIB table, it is then
checked against the adjacency table to ensure the same interface receiving the packet is the
same interface used for the return path
B.
If a packet fails the uRPF loose mode check, the packet is then transmitted and creates a log
message
C.
It is typically used on multipoint interfaces or on routers where asymmetrical routing is used
(packets are received on one interface but the return path is not on the same interface); loose
mode verifies a source address by looking in forwarding information base(FIB).
D.
If a packet fails the uRPF loose mode check, the packet is then dropped
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
routing table.
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.