300-101 Latest Exam Braindumps
Question 1: What are the three modes of Unicast Reverse Path Forwarding?A. strict mode, broadcast mode, and VRF mode
B. strict mode, loose mode, and VRF mode
C. broadcast mode, loose mode, and VRF mode
D. strict mode, loose mode, and broadcast mode
Correct Answer: B
Explanation
Network administrators can use Unicast Reverse Path Forwarding (Unicast RPF) to help limit the
malicious traffic on an enterprise network. This security feature works by enabling a router to verify
the reachability of the source address in packets being forwarded. This capability can limit the
appearance of spoofed addresses on a network. If the source IP address is not valid, the packet is
discarded. Unicast RPF works in one of three different modes: strict mode, loose mode, or VRF mode.
Note that not all network devices support all three modes of operation. Unicast RPF in VRF mode will
not be covered in this document.
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 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.
